Exhaust treatment system and method for treatment of an exhaust stream

ABSTRACT

An exhaust treatment system comprising: a first dosage device, arranged to supply a first additive into said exhaust stream; a first reduction catalyst device, downstream of said first dosage device arranged for reduction of nitrogen oxides in said exhaust stream through the use of said first additive; a particulate filter, at least partly comprising a catalytically oxidizing coating, which is downstream of said first reduction catalyst device to catch soot particles, and to oxidize one or several of nitrogen oxide and incompletely oxidized carbon compounds in said exhaust stream; a second dosage device, downstream of said particulate filter to supply a second additive into said exhaust stream; and a second reduction catalyst device, downstream of said second dosage device for a reduction of nitrogen oxides in said exhaust stream, with the use of at least one of said first and said second additive.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a national stage application (filed under 35 §U.S.C.371) of PCT/SE15/050220, filed Feb. 27, 2015 of the same title, which,in turn claims priority to Swedish Application Nos. 1450229-8 and1450230-6, both filed Feb. 28, 2014 of the same title; the contents ofeach of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an exhaust treatment system, method,and computer program product for treatment of an exhaust stream.

BACKGROUND OF THE INVENTION

The following background description constitutes a description of thebackground to the present invention, and thus need not necessarilyconstitute prior art.

In connection with increased government interests concerning pollutionand air quality, primarily in urban areas, emission standards andregulations regarding emissions from combustion engines have beendrafted in many jurisdictions.

Such emission standards often consist of requirements definingacceptable limits of exhaust emissions from combustion engines in forexample vehicles. For example, emission levels of nitrogen oxidesNO_(x), hydrocarbons C_(x)H_(y), carbon monoxide CO and particles PM areoften regulated by such standards for most types of vehicles. Vehiclesequipped with combustion engines typically give rise to such emissionsin varying degrees. In this document, the invention will be describedmainly for its application in vehicles. However, the invention may beused in substantially all applications where combustion engines areused, for example in vessels such as ships or aeroplanes/helicopters,wherein regulations and standards for such applications limit emissionsfrom the combustion engines.

In an effort to comply with these emission standards, the exhaustscaused by the combustion of the combustion engine are treated(purified).

A common way of treating exhausts from a combustion engine consists of aso-called catalytic purification process, which is why vehicles equippedwith a combustion engine usually comprise at least one catalyst. Thereare different types of catalysts, where the different respective typesmay be suitable depending on for example the combustion concept,combustion strategies and/or fuel types which are used in the vehicles,and/or the types of compounds in the exhaust stream to be purified. Inrelation to at least nitrous gases (nitrogen monoxide, nitrogendioxide), referred to below as nitrogen oxides NO_(x), vehicles oftencomprise a catalyst, wherein an additive is supplied to the exhauststream resulting from the combustion in the combustion engine, in orderto reduce nitrogen oxides NO_(x), primarily to nitrogen gas and aqueousvapor. This is described in more detail below.

SCR (Selective Catalytic Reduction) catalysts are a commonly used typeof catalyst for this type of reduction, primarily for heavy goodsvehicles. SCR catalysts usually use ammonia NH₃, or a composition fromwhich ammonia may be generated/formed, as an additive to reduce theamount of nitrogen oxides NO_(x) in the exhausts. The additive isinjected into the exhaust stream resulting from the combustion engineupstream of the catalyst. The additive added to the catalyst is adsorbed(stored) in the catalyst, in the form of ammonia NH₃, so that aredox-reaction may occur between nitrogen oxides NO_(x) in the exhaustsand ammonia NH₃ available via the additive.

A modern combustion engine is a system where there is cooperation andmutual impact between the engine and the exhaust treatment.Specifically, there is a correlation between the exhaust treatmentsystem's ability to reduce nitrogen oxides NO_(x) and the fuelefficiency of the combustion engine. For the combustion engine, there isa correlation between the engine's fuel efficiency/total efficiency andthe nitrogen oxides NO_(x) produced by it. This correlation specifiesthat for a given system there is a positive correlation between nitrogenoxides NO_(x) produced and fuel efficiency, in other words an enginethat is permitted to emit more nitrogen oxides NO_(x) may be induced toconsume less fuel by way of, for example, a more optimal selection ofthe injection timing, which may yield a higher combustion efficiency.Similarly, there is often a negative correlation between a producedparticle mass PM and the fuel efficiency, meaning that an increasedemission of particle mass PM from the engine is connected with anincreased fuel consumption. This correlation is the background to thewidespread use of exhaust treatment systems comprising an SCR-catalyst,where the intention is the optimization of the engine regarding fuelconsumption and emission of particles, towards a relatively largeramount of nitrogen oxides NO_(x) produced. A reduction of these nitrogenoxides NO is then carried out in the exhaust treatment system, whichthus may also comprise an SCR catalyst. Through an integrated approachin the design of the engine and exhaust treatment system, where theengine and exhaust treatment complement each other, a high fuelefficiency may therefore be achieved jointly with low emissions of bothparticles PM as well as nitrogen oxides NO_(x).

SUMMARY OF THE INVENTION

To some extent, the performance of the exhaust treatment system may beenhanced by increasing the substrate volumes comprised in the exhausttreatment system, which in particular reduces losses due to unevendistribution of the exhaust flow through the substrate. At the sametime, a larger substrate volume provides a greater back pressure, whichmay counteract gains in fuel efficiency due to the higher conversiondegree. Larger substrate volumes also entail an increased cost. It isthus important to be able to use the exhaust treatment system optimally,for example by avoiding oversizing and/or by limiting the exhausttreatment system's spread in terms of size and/or manufacturing cost.

The function and efficiency for catalysts in general, and for reductioncatalysts in particular, is strongly dependent on the temperature overthe reduction catalyst. The term “temperature over the reductioncatalyst” as used herein, means the temperature in/at/for the exhauststream through the reduction catalyst. The substrate will assume thistemperature due to its heat exchanging ability. At a low temperatureover the reduction catalyst, the reduction of nitrogen oxides NO istypically ineffective. The NO₂/NO_(x) fraction in the exhausts providesa certain potential for increasing the catalytic activity, also at lowerexhaust temperatures. The temperature and the NO₂/NO_(x) fraction overthe reduction catalyst are, however, generally difficult to control,since they to a great extent depend on a number of factors, such as howthe driver drives the vehicle. For example, the temperature over thereduction catalyst depends on the torque requested by a driver and/or bya cruise control, on the appearance of the road section in which thevehicle is located, and/or the driving style of the driver.

Prior art exhaust treatment systems, such as the system described indetail below, which many producers have used to meet the emissionstandard Euro VI (hereafter referred to as the “Euro VI-system”),comprising an oxidation catalyst, a diesel particulate filter and areduction catalyst, have problems relating to the large thermalmass/inertia of the catalysts/filters and the large thermal mass/inertiaof the rest of the exhaust treatment system, comprising for exampleexhaust pipes, silencers and various connections. At for example coldstarts, where both the engine and the exhaust treatment system are cold,and at throttle from low exhaust temperatures, where more torque thanpreviously is requested, for example when easy city driving turns intohighway driving, or after idling and power take-off, it is primarily thediesel particulate filter's large thermal mass/inertia that causes thetemperature of the reduction catalyst to increase only slowly in suchprior art exhaust treatment systems. Thus, at for example cold startsand at vehicle operation with temperature- and/or flow transientelements, the function of the reduction catalyst deteriorates, andaccordingly the reduction of nitrogen oxides NO_(x) also deteriorates.This deterioration may result in a poor exhaust purification, riskingunnecessary pollution of the environment. Additionally, because of thedeterioration of the reduction catalyst's function, the risk of notachieving the regulatory requirements relating to exhaust purificationincreases. Fuel consumption may also be adversely impacted by thedeteriorating function, since fuel energy may then need to be used inorder to increase the temperature and efficiency of the reductioncatalyst via different temperature increasing measures.

One objective of the present invention is to improve the purification ofexhausts in an exhaust treatment system, while improving the conditionsfor achieving a higher fuel efficiency.

Through the use of the present invention a more temperature efficienttreatment of the exhausts is achieved, since the first reductioncatalyst device fitted upstream in the exhaust treatment systemaccording to the invention may, in some operating modes, operate at morefavorable temperatures than the temperatures of the second reductioncatalyst device fitted downstream. For example, at cold starts andthrottle from low temperatures, the first reduction catalyst devicesooner reaches operating temperatures, at which an efficient reductionof nitrogen oxides NO_(x) is obtained. Thus, according to the inventionthe available heat is used in a more energy efficient manner, resultingin an earlier and/or more efficient reduction of nitrogen oxides NO_(x),for example at cold starts and at throttle from low exhausttemperatures, than what would have been possible with the abovedescribed prior art exhaust treatment systems.

At certain other operating modes, similarly, the second reductioncatalyst device fitted downstream may operate at more favorabletemperatures than the temperatures of the first reduction catalystdevice fitted upstream.

Through the use of the invention different thermal inertias are obtainedfor the first and the second reduction catalyst device, meaning thatthese first and second reduction catalyst devices may be optimizeddifferently with respect to activity and selectivity. Thus, the firstand second reduction catalyst devices may be optimized from a systemperspective, that is to say from a perspective relating to the entireexhaust treatment system's function, and may therefore be used toprovide an overall more efficient purification of the exhausts than whatthe separate optimized catalysts would have been able to provide. Suchoptimization of the first and second reduction catalyst devicesaccording to the invention may be used to provide this overall moreefficient purification at for example cold start, but also atsubstantially all vehicle operation, since the temperature- and/or flowtransient elements often occur also at normal vehicle operation. Asmentioned above, the invention may also be used for exhaust purificationin other units than vehicles, such as in different types of vessels,where an overall more efficient purification of the exhausts from theunit is obtained.

The present invention uses the thermal inertia/mass of the particulatefilter to the function's advantage, by optimizing the function for boththe first and the second reduction catalyst devices, based on thisinertia. Accordingly, through the present invention acooperation/symbiosis is obtained between the first reduction catalystdevice, which is optimized for the first thermal mass and the firsttemperature function/temperature process to which it is exposed, and thesecond reduction catalyst device, which is optimized for the secondthermal mass and the second temperature process to which it is exposed.

The first reduction catalyst device and/or the second reduction catalystdevice may thus be optimized based on characteristics, for examplecatalytic characteristics, for the second reduction catalyst deviceand/or the first reduction catalyst device. For example, the secondreduction catalyst device may be construed/selected so that itscatalytic characteristics at low temperatures become less efficient,facilitating that its catalytic characteristics at high temperatures maybe optimized. If these catalytic characteristics of the second reductioncatalyst device are taken into account, the first reduction catalystdevice's catalytic characteristics may then be optimized in such a waythat it need not be as efficient at high temperatures.

These possibilities of optimizing the first reduction catalyst deviceand/or the second reduction catalyst device mean that the presentinvention provides an exhaust purification which is suitable foremissions arising at substantially all types of driving modes,especially for highly transient operation, which results in a variabletemperature- and/or flow profile. Transient operation may, for example,comprise relatively many starts and brakes of the vehicle, or relativelymany uphill and downhill slopes. Since relatively many vehicles, such asfor example buses that often stop at bus stops, and/or vehicles drivenin urban traffic or hilly topography, experience such transientoperation, the present invention provides an important and very usefulexhaust purification, which overall reduces the emissions from thevehicles in which it is implemented.

The present invention thus uses the previously problematic thermal massand heat exchange in, primarily, the particulate filter in the EuroVI-system as a positive characteristic. The exhaust treatment systemaccording to the present invention may, similarly to the Euro VI-system,contribute with heat to the exhaust stream and the reduction catalystdevice fitted downstream for brief dragging periods, or other lowtemperature operation, if such low temperature operation was preceded byoperation with higher operating temperatures. Due to its thermalinertia, the particulate filter at this point is warmer than the exhauststream, and accordingly the exhaust stream may be heated by theparticulate filter.

Additionally, this good characteristic is complemented by the fact thatthe reduction catalyst device placed upstream may, especially attransient operation, use the higher temperature arising in connectionwith throttle. Thus, the first reduction catalyst device experiences ahigher temperature after the throttle, than what the second reductioncatalyst device experiences. Such higher temperature for the firstreduction catalyst device is used by the present invention in order toimprove the NO_(x)-reduction of the first reduction catalyst device. Thepresent invention, which uses two reduction catalyst devices, may useboth these positive characteristics by adding a possibility forNO_(x)-reduction with a small thermal inertia, that is to say theexhaust treatment system according to the invention comprises both aNO_(x)-conversion upstream of a large thermal inertia, and aNO_(x)-conversion downstream of a large thermal inertia. The exhausttreatment system according to the present invention may then, in anenergy efficient manner, use available heat to a maximum, meaning thatthe rapid and “unfiltered” heat experienced by the reduction catalystdevice placed upstream may also be used to make the exhaust treatmentsystem according to the invention efficient.

The exhaust treatment system according to the present invention haspotential to meet the emission requirements in the Euro VI emissionstandard. Additionally, the exhaust treatment system according to thepresent invention has potential to meet the emission requirements inseveral other existing and/or future emission standards.

The exhaust treatment system according to the present invention may bemade compact, since it comprises, in relation to theperformance/purification degree which it may deliver, few units in theexhaust treatment system. These relatively few units need not, for abalanced exhaust treatment system according to the present invention,have a large volume. Since the number of units, and the size of theseunits, is minimized by the present invention, the exhaust back pressuremay also be limited, which entails a lower fuel consumption for thevehicle. Catalytic performance per substrate volume unit may beexchanged for a smaller substrate volume, in order to obtain a certaincatalytic purification. For an exhaust purification device with apredetermined size, and/or a predetermined external geometry, which isoften the case in vehicles with limited space for the exhaust treatmentsystem, a smaller substrate volume means that a larger volume within thepredetermined size of the exhaust purification may be used fordistribution, mixture and turnings of the exhaust stream within theexhaust purification device. This means that the exhaust back pressuremay be reduced for an exhaust purification device with a predeterminedsize and/or a predetermined external geometry, if the performance persubstrate volume unit is increased. Thus, the total volume of theexhaust treatment system according to the invention may be reduced,compared with at least some prior art systems. Alternatively, theexhaust back pressure may be reduced with the use of the presentinvention.

At the use of the present invention, the need for an exhaust gasrecirculation system (Exhaust Gas Recirculation; EGR) may also bereduced or eliminated. A reduction of the need to use an exhaust gasrecirculation system has advantages, among others relating torobustness, gas exchange complexity and power output.

At new production of vehicles, the system according to the presentinvention may be fitted easily at a limited cost, since the separateoxidation catalyst DOC, that is to say the separate substrate for theoxidation catalyst DOC, and the installation of such substrate whichexisted in prior art systems, is exchanged for the first reductioncatalyst device according to the present invention at manufacture.Retrofitting of an exhaust treatment system according to the presentinvention may also be carried out easily, since the oxidation catalystDOC, which was present in prior art systems, may also be replaced withthe first reduction catalyst device according to the present inventionin already produced vehicles. An additional dosage device will berequired. It may also be needful to replace the particulate filter or toadjust the characteristics of its catalytic coating. In order to achievea sufficient nitrogen dioxide based (NO₂-based) soot oxidation, theengine's ratio between nitrogen oxides and soot (NO_(x)/soot-ratio), andthe control of the reductant dosage, effected with the first dosagedevice, fitted upstream in the exhaust treatment system according to theinvention, may need to fulfil certain criteria.

The oxidizing coating, for example comprising precious metal, which inEuro VI-systems is located in the oxidation catalyst DOC, may accordingto one embodiment of the invention at least partly be implemented, forexample, in the diesel particulate filter DPF, whereat conditions for asufficient NO₂-based soot oxidation may be obtained. Thus, a compactdesign of the exhaust treatment system according to the invention isobtained. Through the use of a diesel particulate filter DPF withoxidation catalyst characteristics, an increased predictability for theformation of nitrogen dioxides NO₂ may also be obtained. This is due tothe fact that deactivation of the catalytically active seats, such asfor example deactivation caused by phosphorus, often has an axialconcentration gradient. This means that catalysts with a relativelybrief physical length may be more sensitive to these intoxications, thancatalysts with a larger physical length. Where for example preciousmetal, such as platinum, is placed on the physically long dieselparticulate filter DPF, instead of on the physically shorter firstoxidation catalyst DOC, more stable levels of nitrogen dioxide NO₂ maypotentially be obtained over time.

According to one embodiment of the present invention, the firstreduction catalyst device constitutes an, at least partly, protectivesubstrate upstream of an oxidizing coating, wherein the oxidizingcoating may be comprised in a particulate filter, coated with forexample a precious metal. The catalytic coating for the first reductioncatalyst device may, according to one embodiment, be selected to berobust in withstanding chemical poisoning, which may, over time, providea more stable level for the ratio between nitrogen dioxide and nitrogenoxides NO₂/NO_(x) reaching the second reduction catalyst device. Thecatalytic coating protected may also, according to one embodiment, becomprised in a so-called combicat, which is described in more detailbelow.

The present invention also has an advantage in that two cooperatingdosage devices are used in combination for the dosage of a reductant,for example urea, upstream of the first and second reduction catalystdevices, which relieves and facilitates mixture and potentialevaporation of the reductant, since the injection of the reductant isdivided between two physically separate positions. This reduces the riskof the reductant cooling down the exhaust treatment system locally,which may potentially form deposits at the positions where the reductantis injected, or downstream of such positions.

The relief of vaporization of the reductant means that the exhaust backpressure may potentially be reduced, since the requirement forNO_(x)-conversion per reduction step is reduced, so that the amount ofreductant that must be vaporized is also reduced, since the injection ofthe reductant is divided between two positions, compared to the previoussingle dosage position. It is also possible, with the present invention,to reduce, or to completely shut off dosage in one dosage position, andthen to remove potential precipitates that may arise, using heat.Accordingly, for example a larger dosage amount (a more ample dosage)may be allowed in the first dosage position for the first reductioncatalyst device, since potential precipitates may be removed with heatat the same time as the emission requirements are met by the secondreduction catalyst device during this time. This larger/more ampledosage may be viewed as a more aggressive dosage, providing dosageamounts closer to/above a dosage threshold value at which a risk ofprecipitates/crystallisations of additive arises.

A non-limiting example may be that, if the single dosage device in theEuro VI-system had been optimized to provide a vaporization and adistribution of the reductant providing a 98% NO_(x)-conversion, theNO_(x)-conversion of the two respective reduction catalyst devices inthe exhaust treatment system according to the present invention may bereduced, for example to 60% and 95%, respectively. The amounts ofreductant, which in this case have to be vaporized in the respective twopositions become lower, and the allocations of reductant need not be asoptimized in the system according to the invention as in the EuroVI-system. An optimal and homogeneous distribution of reductant, asrequired by the Euro VI-system, often results in a high exhaust backpressure, since an advanced vaporization/mixture must be used when thereductant is mixed with the exhausts, that is to say with the nitrogenoxides NO_(x). Since the requirements for an optimal and homogeneousdistribution of reductant are not as high in relation to the systemaccording to the present invention, there is a possibility of reducingthe exhaust back pressure when the present invention is used.

The two dosage positions used in the present invention thus facilitatethat, overall, more additive may be supplied to the exhaust stream, thanif only one dosage position had been used in the system. This means animproved performance may be provided.

The present invention thus provides a removal of load for the mixing andthe potential vaporization. The double dosage positions mean, on the onehand, that the reductant is mixed and potentially vaporized in twopositions, instead of in one position as in the Euro VI-system and, onthe other hand, the double dosage positions mean that lower conversionlevels, and thus a dosage with a less unfavorable ratio, may be used.The influence of the size of the conversion level and the ratio of thedosage is described in further detail below.

For embodiments which use additives in liquid form, the vaporization isalso improved, when the system according to the invention is used. Thisis because, on the one hand, the total amount of additive to be suppliedto the exhaust stream is split in two physically separate dosagepositions and, on the other hand, the system may be loaded more heavilythan systems with only one dosage position. The system may be loadedmore heavily since the dosage in the position where residue of additivepotentially arises may, where needed, be reduced/closed with the systemaccording to the invention, while criteria for the total emissionssimultaneously may be met.

The exhaust treatment system according to the present invention alsoprovides for a robustness against errors in the dosage amounts ofreductant. According to one embodiment of the present invention, anNO_(x)-sensor is placed between the two dosage devices in the exhausttreatment system. This means it is possible to correct a potentialdosage error at the first dosage device, in connection withadministration of a dose with the second dosage device.

Table 1 below shows a non-limiting example of conversion levels andemissions, which are the result of a 10% dosage error for the reductantin a case with 10 g/kWh NO_(x). In the system with one reduction step,according to the example a 98% conversion of NO_(x) is requested. Inorder to provide a 98% conversion of NO_(x) in the exhaust treatmentsystem with two reduction steps, a 60% conversion of NO_(x) is requestedfor the first reduction catalyst device, and a 95% conversion of NO_(x)is requested for the second reduction catalyst device. As illustrated inthe table, a system with one reduction step, such as in the EuroVI-system, results in a 1.18 g/kWh emission. Two reduction steps, suchas in a system according to the present invention, instead result in theemission of 0.67 g/kWh according to the example. This considerably lowerresulting emission for the system according to the present invention isthe mathematical result of the use of the two dosage points/reductionsteps, as illustrated by Table 1. The NO_(x)-sensor placed between thetwo dosage devices provides for this possibility of correcting for thedosage error at the first dosage device, in connection with the dosagewith the second dosage device.

TABLE 1 Requested Transformation Emissions transformation ratio achievedwith achieved ratio 10% dose inaccuracy [g/kWh] One reduction step 98%88.2% 1.18 Two reduction steps 98% Step 1 - 60% 54.0% 4.60 Step 2 - 95%85.5% 0.67

This embodiment may be implemented with a low level of added complexity,since an NO_(x)-sensor, which is already present in today's EuroVI-system, may be used in connection with the correction. TheNO_(x)-sensor normally sits in the silencer inlet. Since the firstreduction catalyst device and its first dosage in the present inventiondoes not necessarily need to remove all nitrogen oxides NO_(x) from theexhaust stream, the first reduction catalyst device, and its firstdosage, may potentially cope without any measured information aboutnitrogen oxides NO_(x) upstream of the first reduction catalyst device.However, it is important to obtain correct information, that is to sayinformation with relatively high accuracy, about nitrogen oxides NO_(x)upstream of the second reduction catalyst device, since the emissions inthe second reduction catalyst device must be reduced to low levels,often to levels near zero. This position, i.e. the position at orupstream of the second reduction catalyst device, should therefore,according to one embodiment of the invention, suitably be equipped witha NO_(x)-sensor. Such NO_(x)-sensor may thus, according to theembodiment, be placed downstream of the particulate filter, which isalso a less aggressive environment from a chemical poisoningperspective, compared to the environment upstream of the particulatefilter.

Additionally, an adaptation/calibration of several NO_(x)-sensors in theexhaust treatment system may easily be carried out in the systemaccording to the present invention, since the sensors may be subjectedto the same NO_(x)-level, at the same time as the emission levels may bekept at reasonable levels during the adaptation/calibration. For theEuro VI-system, for example, the adaptation/calibration often entailsthat the emissions become too high during, and also partly after, theadaptation/calibration itself.

As mentioned above, the first and second reduction catalyst devices maybe optimized individually, and with consideration of the entire exhausttreatment system's function, which may result in an overall veryefficient purification of the exhausts. This individual optimization mayalso be used to reduce one or several of the volumes taken up by thefirst and second reduction catalyst devices, so that a compact exhausttreatment system is obtained.

For the above mentioned non-limiting example, where NO_(x)-conversioncorresponding to the two respective dosage devices in the exhausttreatment system according to the present invention may constitute 60%or 95%, respectively, the exhaust treatment system according to theinvention theoretically requires a total volume for the first and secondreduction catalyst devices, equaling the size required of the reductioncatalyst device in the Euro VI-system, to provide a NO_(x)-conversionrepresenting 98% with only one reduction catalyst.

In practice, however, the Euro VI-system's requirement regarding thehigh 98% conversion level means that a larger catalyst volume isrequired than catalyst volumes representing the sum of the lowerconversion levels 60% and 95%, respectively, according to the presentinvention's requirements. This is due to the non-linear relationshipbetween volume and conversion level. At high conversion levels, such asfor example 98%, imperfections in the distribution of exhausts and/orreductant impact the requirement for catalyst volume to a greaterextent. High conversion levels also require a larger catalyst volume,since the high conversion levels result in a greater deposition/coverlevel of reductant on the catalyst surface. There is a risk that suchdeposited reductant may then desorb at some exhaust conditions, i.e. aso-called ammonia-slip may arise.

One example of the effect of the distribution of reductant and theeffect of the increasing NH₃-slip is illustrated in FIG. 6. The figureshows that the ratio, that is to say the gradient/derivative, for theconversion level (y axis to the left) decreases in relation tostoichiometry (x axis) at high conversion levels, that is to say thatthe curve for the conversion level planes out for high conversionlevels, which among others is due to imperfections in the distributionof exhausts and/or reductant. The figure also shows that an increase ofNH₃-slip (y axis to the right) arises at higher conversion levels. Athigher values than one (1) for the stoichiometry, more reductant isadded than theoretically needed, which also increases the risk ofNH₃-slip.

The present invention also facilitates, according to one embodiment,control of a ratio NO₂/NO_(x), between the amount of nitrogen dioxideNO₂ and the amount of nitrogen oxides NO_(x), for the second reductionstep, which means that the system may avoid excessively high values forthis ratio, for example avoiding NO₂/NO_(x)>50%, and that the system, byincreasing the dosage, may increase the value for the ratio NO₂/NO_(x)when the value is too low, for example if NO₂/NO_(x)<50%. The value forthe ratio NO₂/NO_(x) may here, for example through the use of anembodiment of the present invention, be increased by reducing the levelof nitrogen oxides NO_(x). The ratio NO₂/NO_(x) may assume lower values,for example, after the system has aged for some time. The presentinvention thus provides for a possibility to counteract thischaracteristic of deterioration over time, which is negative to thesystem, and results in values that are too low for the ratio NO₂/NO_(x).Through the use of the present invention, the level of nitrogen dioxideNO₂ may thus be controlled actively, which is possible since theNO_(x)-level may be adjusted upstream of the catalytically oxidizingcoating, for example comprising precious metal, in the particulatefilter 320. This control of the ratio NO₂/NO_(x) may, apart fromadvantages in catalytic performance, such as higher NO_(x)-conversion,also result in a possibility of specifically reducing emissions ofnitrogen dioxide NO₂, which result in a very poisonous and strongsmelling emission. This may result in advantages at a potential futureintroduction of a separate regulatory requirement relating to nitrogendioxide NO₂, and facilitate a reduction of harmful emissions of nitrogendioxide NO₂. This may be compared with for example the Euro VI-system,in which the fraction of nitrogen dioxide NO₂ provided at the exhaustpurification may not be impacted in the exhaust treatment system itself.

In other words, the active control of the level of nitrogen dioxide NO₂is facilitated at the use of the present invention, where the activecontrol may be used to increase the level of nitrogen dioxide NO₂ indriving modes for which this is necessary Accordingly, an exhausttreatment system may be selected/specified, which for example requiresless precious metal and thus also is cheaper to manufacture.

If the fraction of the total conversion of nitrogen oxides NO_(x)occurring via a rapid reaction path, that is to say via a fast SCR,wherein the reduction occurs via reaction paths over both nitrogen oxideNO and nitrogen dioxide NO₂, may be increased through active control ofthe level of nitrogen dioxide NO₂, then the catalyst volume requirementdescribed above may also be reduced. According to one embodiment of thepresent invention, the first reduction catalyst device in the exhausttreatment system is active at a lower reduction temperature intervalT_(red) than the oxidation temperature interval T_(ox), required for thenitrogen dioxide based soot oxidation in the particulate filter cDPF. Asan example, the nitrogen dioxide based soot oxidation in the particulatefilter DPF may occur at temperatures exceeding 275° C. Hereby, thereduction of nitrogen oxides NO_(x) in the first reduction catalystdevice does not significantly compete with the soot oxidation in theparticulate filter DPF, since they are active within at least partlydifferent temperature intervals T_(red)≠T_(ox). For example, a wellselected and optimized first reduction catalyst device may result in asignificant conversion of nitrogen oxides NO_(x) at approximately 200°C., which means that this first reduction catalyst device does not needto compete with the particulate filter's soot oxidation performance.

With the use of the present invention, secondary emissions such asemissions of ammonia NH₃ and/or nitrous oxide (laughing gas) N₂O may bereduced in relation to a given conversion level, and/or a givenNO_(x)-level. A catalyst, for example an SC (Slip Catalyst), which maybe comprised in the second reduction step if the emissions for certainjurisdictions must be reduced to very low levels, may have a certainselectivity against, for example, nitrous oxide N₂O, which means thatthe reduction of the NO_(x)-level through the use of the additionalreduction step according to the present invention also shifts theresulting levels for nitrous oxide N₂O downwards. The resulting levelsfor ammonia NH₃ may be shifted downwards in a similar way, when thepresent invention is used.

Through the use of the present invention a better fuel optimization maybe obtained for the vehicle, since there is thus potential to controlthe engine in a more fuel efficient manner, so that a higher efficiencyfor the engine is obtained. Thus, a performance gain and/or a reducedemission of carbon dioxide CO₂ may be obtained when the presentinvention is used.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be illustrated in more detail below, along with theenclosed drawings, where similar references are used for similar parts,and where:

FIG. 1 shows an example vehicle which may comprise the presentinvention,

FIG. 2 shows a traditional exhaust treatment system,

FIG. 3 shows an exhaust treatment system according to the presentinvention,

FIG. 4 shows a flow chart for the method for exhaust treatment accordingto the invention,

FIG. 5 shows a control device according to the present invention,

FIG. 6 shows among others a ratio between NO_(x)-conversion andNH₃-slip, and

FIG. 7 schematically shows a multifunctional slip-catalyst.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically shows an example vehicle 100 comprising an exhausttreatment system 150, which may be an exhaust treatment system 150according to one embodiment of the present invention. The powertraincomprises a combustion engine 101, which in a customary manner, via anoutput shaft 102 on the combustion engine 101, usually via a flywheel,is connected to a gearbox 103 via a clutch 106.

The combustion engine 101 is controlled by the engine's control systemvia a control device 115. Likewise, the clutch 106 and the gearbox 103may be controlled by the vehicle's control system, with the help of oneor more applicable control devices (not shown). Naturally, the vehicle'spowertrain may also be of another type, such as a type with aconventional automatic gearbox, of a type with a hybrid powertrain, etc.

An output shaft 107 from the gearbox 103 drives the wheels 113, 114 viaa final drive 108, such as e.g. a customary differential, and the driveshafts 104, 105 connected to said final drive 108.

The vehicle 100 also comprises an exhaust treatment system/exhaustpurification system 150 for treatment/purification of exhaust emissionsresulting from combustion in the combustion chamber of the combustionengine 101, which may consist of cylinders.

FIG. 2 shows a prior art exhaust treatment system 250, which mayillustrate the above mentioned Euro VI-system, and which is connected toa combustion engine 201 via an exhaust conduit 202, wherein the exhaustsgenerated at combustion, that is to say the exhaust stream 203, isindicated with arrows. The exhaust stream 203 is led to a dieselparticulate filter (DPF) 220, via a diesel oxidation catalyst (DOC) 210.During the combustion in the combustion engine, soot particles areformed, and the particulate filter 220 is used to catch these sootparticles. The exhaust stream 203 is here led through a filterstructure, wherein soot particles from the exhaust stream 203 are caughtpassing through, and are stored in the particulate filter 220.

The oxidation catalyst DOC 210 has several functions and is normallyused primarily to oxidize, during the exhaust treatment, remaininghydrocarbons C_(x)H_(y) (also referred to as HC) and carbon monoxide COin the exhaust stream 203 into carbon dioxide CO₂ and water H₂O. Theoxidation catalyst DOC 210 may also oxidize a large fraction of thenitrogen monoxides NO occurring in the exhaust stream into nitrogendioxide NO₂. The oxidation of nitrogen monoxide NO into nitrogen dioxideNO₂ is important to the nitrogen dioxide based soot oxidation in thefilter, and is also advantageous at a potential subsequent reduction ofnitrogen oxides NO_(x). In this respect, the exhaust treatment system250 further comprises an SCR (Selective Catalytic Reduction) catalyst230, downstream of the particulate filter DPF 220. SCR catalysts useammonia NH₃, or a composition from which ammonia may begenerated/formed, e.g. urea, as an additive for the reduction ofnitrogen oxides NO_(x) in the exhaust stream. The reaction rate of thisreduction is impacted, however, by the ratio between nitrogen monoxideNO and nitrogen dioxide NO₂ in the exhaust stream, so that the reductivereaction is impacted in a positive direction by the previous oxidationof NO into NO₂ in the oxidation catalyst DOC. This applies up to a valuerepresenting approximately 50% of the molar ratio NO₂/NO_(x). For higherfractions of the molar ratio NO₂/NO_(x), that is to say for valuesexceeding 50%, the reaction speed is impacted in a strongly negativemanner.

As mentioned above, the SCR-catalyst 230 requires additives to reducethe concentration of a compound, such as for example nitrogen oxidesNO_(x), in the exhaust stream 203. Such additive is injected into theexhaust stream upstream of the SCR-catalyst 230 (not shown in FIG. 2).Such additive is often ammonia and/or urea based, or consists of asubstance from which ammonia may be extracted or released, and may forexample consist of AdBlue, which basically consists of urea mixed withwater. Urea forms ammonia at heating (thermolysis) and at heterogeneouscatalysis on an oxidizing surface (hydrolysis), which surface may, forexample, consist of titanium dioxide TiO2, within the SCR-catalyst. Theexhaust treatment system may also comprise a separate hydrolysiscatalyst.

The exhaust treatment system 250 is also equipped with a slip-catalyst(SC), which is arranged to oxidize a surplus of ammonia that may remainafter the SCR-catalyst 230, and/or to assist the SCR-catalyst withfurther reduction of NO_(x). Accordingly, the slip-catalyst SC mayprovide a potential for improving the system's totalconversion/reduction of NOx.

The exhaust treatment system 250 is also equipped with one or severalsensors, such as one or several NO_(x)- and/or temperature sensors 261,262, 263, 264 for the determination of nitrogen oxides and/ortemperatures in the exhaust treatment system.

The prior art exhaust treatment system shown in FIG. 2, that is to saythe Euro VI-system, has a problem in that catalysts are efficient heatexchangers, which jointly with the rest of the exhaust system,comprising for example the exhaust conduit 202, as well as material andspace for silencing and various connections, has a substantial thermalmass/inertia. At starts where the catalyst temperature is below itsoptimal operating temperature, which may for example be approximately300° C., and at a throttle from low exhaust temperatures, which may forexample occur when light city driving transitions into motorway driving,or after idling and power take-off, the exhaust temperature is filteredby this large thermal mass. Accordingly, the function, and therefore theefficiency of the reduction, is impacted by for example nitrogen oxidesNO_(x) in the SCR-catalyst 230, which may entail that a poor exhaustpurification is provided by the system shown in FIG. 2. This means thata smaller amount of emitted nitrogen oxides NO_(x) may be permitted tobe released from the engine 101, compared to if the exhaust purificationhad been more efficient, which may lead to requirements for a morecomplex engine and/or a lower fuel efficiency.

In the prior art exhaust treatment system there is also a risk that therelatively cold reductant cools down the exhaust pipe parts locally, andmay thereby give rise to precipitates. This risk of precipitatesdownstream of the injection increases if the injected amount ofreductant must be large.

Among others to compensate for the limited availability ofheat/temperature at, for example, cold starts and operation with a lowload, a so-called fast SCR may be used, controlling reduction, so thatit occurs to as great an extent as possible via reaction paths over bothnitrogen oxide NO and nitrogen dioxide NO₂. With a fast SCR, thereaction uses equal parts of nitrogen monoxide NO and nitrogen dioxideNO₂, which means that an optimal value of the molar ration NO₂/NO_(x) isnear 50%.

In some conditions regarding the catalyst temperature and flow, i.e. fora certain dwell-time in the catalyst (“Space Velocity”), there is a riskthat a non-advantageous fraction of nitrogen dioxides NO₂ is obtained.Specifically, there is a risk that the ratio NO₂/NO_(x) exceeds 50%,which may constitute a real problem for exhaust purification. Anoptimization of the ratio NO₂/NO_(x) for the above mentioned criticallow temperature operating modes, therefore risks providing too high afraction of nitrogen dioxides NO₂ in other operating modes, at forexample higher temperatures. This higher fraction of nitrogen dioxidesNO₂ results in a greater volume requirement for the SCR-catalyst, and/orin a limitation of the amount of nitrogen oxides released from theengine, and accordingly in a poorer fuel efficiency for the vehicle.Additionally, there is a risk that the higher fraction of nitrogendioxides NO₂ also results in emissions of laughing gas N₂O. These risksof a non-advantageous fraction of nitrogen dioxide NO₂ arising alsoexist due to the system's ageing. For example, the ratio NO₂/NO_(x) mayassume lower values when the system has aged, which may entail that acatalyst specification, which results in too high fractions ofNO₂/NO_(x) in a non-aged state, must be used to compensate for ageing.

A poor control robustness against dosage errors regarding the amount ofreductant and/or a poor control robustness against a sensor error mayalso constitute a problem for the exhaust treatment system at highNO_(x)-conversion levels.

In the prior art solution described in US2005/0069476, it is suggestedthat the exhaust system must consist of a close connected SCR-catalyst(ccSCR), which shall be connected near, less than 1 metre away from, theengine's or the turbo's exhaust outlet, followed by an SCRT-systemdownstream. The SCRT-system is defined by the authors of US2005/0069476as a prior art system in the direction of the exhaust stream, comprisinga DOC-catalyst, a DPF-filter, a urea dosage device, and an SCR-catalyst.Thus, the exhaust treatment system described in US2005/0069476 consistsof the following sequential, separate components in the direction of theexhaust stream's flow: the close connected ccSCR-catalyst, theDOC-catalyst, the DPF-filter, and the SCR-catalyst; ccSCR-DOC-DPF-SCR.

According to the solution in US2005/0069476 the close connectedccSCR-catalyst must be fitted near the engine and/or the turbo, in orderfor the impact of the thermal mass/inertia of the exhaust pipe, and/orof the exhaust treatment system, to be minimized, since such thermalmass/inertia deteriorates the exhaust treatment system's exhaustpurifying characteristics. Nevertheless, there is a risk that thesolution described in US2005/0069476 may experience performanceproblems, since neither the close connected ccSCR-catalyst nor thesubsequent SCR-catalyst are optimized for cooperative exhaustpurification. The subsequent SCR-catalyst in US2005/0069476 is the samecatalyst as was previously used in the SCRT-system, which means thatthis subsequent SCR-catalyst may become unnecessarily expensive as wellas not being optimal for cooperative exhaust purification with ccSCR.

In US2005/0069476 the close connected ccSCR-catalyst is added to theexhaust treatment system to take care of problems related to the coldstart, which results in a costly solution geared only toward coldstarts, wherein such solution, because it contains an extra device (theccSCR-catalyst) potentially increases the back pressure in the exhausttreatment system, and therefore potentially also increases fuelconsumption. Potentially, the fuel consumption thus increases atoperation other than cold starts, such as for example at motorwayoperation, which entails a higher power output and an often greatercontribution to the total fuel consumption.

These problems for the system described in US2005/0069476 are resolvedat least partly by the present invention.

FIG. 3 schematically shows an exhaust treatment system 350, which isconnected via an exhaust pipe 302 to a combustion engine 301. Exhaustsgenerated at combustion in the engine 301 and the exhaust stream 303(indicated with arrows) are led to a first dosage device 371, arrangedto add a first additive into the exhaust stream 303. A first reductioncatalyst device 331 is arranged downstream of the first dosage device371. The first reduction catalyst device 331 is arranged to reducenitrogen oxides NO_(x) in the exhaust stream 303, through the use of thefirst additive added to the exhaust stream by the first dosage device371. In more detail, the first reduction catalyst device 371 uses anadditive, for example ammonia NH₃, or a substance from which ammonia maybe generated/formed/released, for the reduction of nitrogen oxidesNO_(x) in the exhaust stream 303. This additive may for example consistof the above mentioned AdBlue.

According to one embodiment of the invention, a first hydrolysiscatalyst, which may consist of substantially any suitable hydrolysiscoating, and/or a first mixer, may be arranged in connection with thefirst dosage device 371. The first hydrolysis catalyst, and/or the firstmixer, are then used to increase the speed of the decomposition of ureainto ammonia, and/or to mix the additive with the emissions, and/or tovaporize the additive.

The exhaust treatment system 350 according to the present inventioncomprises a particulate filter 320, which at least partly comprises acatalytically oxidizing coating, downstream of the first reductioncatalyst device 331. The particulate filter 320 is thus arranged both tocatch and to oxidize soot particles, and to oxidize one or several ofnitrogen oxides NO and incompletely oxidized carbon compounds in theexhaust stream 303. The exhaust stream 303 is here led through thefilter structure of the particulate filter, which is at least partlycoated with a catalytically oxidizing material. The soot particles fromthe exhaust stream 303 passing through are caught in the filterstructure, and are stored and oxidized in the particulate filter.

According to one embodiment of the invention, the particulate filter 320is arranged so that the particulate filter 320 is the first exhausttreatment system component reached by the exhaust stream 303, after ithas passed the first reduction catalyst device 331. In other words, theparticulate filter 320 according to the embodiment is connecteddownstream of the reduction catalyst device 331, without anyintermediate exhaust treatment system components, except potentialconduit connections between the reduction catalyst device 331 and theparticulate filter 320.

As described in more detail below, according to one embodiment, thefirst reduction catalyst device 331 may comprise a first selectivecatalytic reduction catalyst SCR₁, a first selective catalytic reductioncatalyst SCR₁, followed downstream by a first slip-catalyst SC₁₁, or afirst selective catalytic reduction catalyst SCR₁ combined with anoxidizing coating in the outlet part on the same substrate. When theparticulate filter 320 is the first exhaust treatment system componentreached by the exhaust stream 303 after it has passed the firstreduction catalyst device 331, substantially no oxidation of nitrogenoxide NO and/or incompletely oxidized carbon compounds occurs betweenthe first reduction catalyst device 331 and the particulate filter 320.

One advantage with connecting the particulate filter 320 downstream ofthe reduction catalyst device 331, without any intermediate exhausttreatment system components, apart from potential pipe connections, isthat the number of substrates in the exhaust treatment system 350 issmaller, than if for example the oxidation catalyst DOC had beenarranged between the particulate filter 320 and the reduction catalystdevice 331. Fewer substrates result in a possibility for a more compactexhaust treatment system 350, with lower back pressure, which is simplerand cheaper to manufacture and/or fit. In such an exhaust treatmentsystem 350, the first reduction catalyst device 331 provides aprotection for the oxidizing coating of the particulate filter placedupstream, which may result in a chemical robustness. The chemicalrobustness is also reinforced by the substrate in the particulate filter320, that is to say the catalytically oxidizing coating in theparticulate filter, being relatively physically long, according to oneembodiment of the invention.

The particulate filter cDPF 320 is, at least partly, coated with acatalytically oxidizing coating, wherein such oxidizing coating maycomprise at least one precious metal. That is to say, the particulatefilter 320 may, at least partly, be coated with one or several preciousmetals, for example platinum. According to one embodiment of the presentinvention, the coating of the filter is arranged in the front part ofthe filter, that is to say in connection with the filter's inlet. Thismay also be expressed as though the coating, for example comprising oneor several precious metals, being placed at that end of the filter,where the exhaust stream flows into the filter. The particulate filtercDPF 320, comprising the oxidizing coating, has several advantagescompared to a classic particulate filter DPF, without an oxidizingcoating.

The particulate filter cDPF 320, comprising the oxidizing coating, leadsto an improved NO₂-based regeneration of the filter, that is to say toan improved NO₂-based soot oxidation, which may also be referred to as apassive regeneration of the filter. In an exhaust treatment systemcomprising a particulate filter DPF, that is to say without an oxidizingcoating, and which does not have an oxidation catalyst DOC between thereduction catalyst and the classic particulate filter DPF, a verylimited NO₂-based oxidation of soot in the filter is obtained.

The system according to the embodiment of the present invention relatesto, through the use of the filter with the oxidizing coating, cleaningthe filter of soot through the NO₂-based passive regeneration/oxidation.However, the present invention may also advantageously be used inconnection with active regeneration of the filter, which is to say whenthe regeneration is initiated by an injection of fuel upstream of thefilter, for example through the use of an injector. At an activeregeneration the exhaust treatment system according to the invention hasone advantage in that the first reduction catalyst device may itselfcope with a certain NO_(x)-conversion, while the second reductioncatalyst device, arranged downstream of the filter, due to theregeneration experiences such a high temperature that it hasdifficulties in achieving a high conversion level.

At the use of the engine's injection system at a regeneration of theparticulate filter cDPF, the first reduction catalyst device will atleast partly assist the particulate filter cDPF with partly oxidizingthe fuel into primarily carbon monoxide CO. Thus, the regeneration ofthe particulate filter cDPF is simplified, compared to exhaust treatmentsystems which do not have a first reduction catalyst device according tothe present invention.

The particulate filter cDPF 320, which comprises the oxidizing coating,also results in more stable conditions for the nitrogen dioxide levelNO₂ at the second reduction catalyst device 332. Additionally, the useof the particulate filter cDPF 320, comprising the oxidizing coating,means that the value for the ratio NO₂/NO_(x), that is to say the levelof NO₂, may be controlled.

The particulate filter 320, which at least partly comprises acatalytically oxidizing coating, may also oxidize soot particles and oneor several incompletely oxidized nitrogen and/or carbon compounds moreefficiently, thanks to the oxidizing coating.

Downstream of the particulate filter 320, the exhaust treatment system350 is equipped with a second dosage device 372, which is arranged tosupply a second additive to the exhaust stream 303, where such secondadditive comprises ammonia NH₃, or a substance, for example AdBlue, fromwhich ammonia may be generated/formed/released, as described above. Thesecond additive may here consist of the same additive as the abovementioned first additive, that is to say that the first and secondadditives are of the same type and may possibly also come from the sametank. The first and second additives may also be of different types andmay come from different tanks.

According to one embodiment of the invention, a second hydrolysiscatalyst and/or a second mixer may also be arranged in connection withthe second dosage device 372. The function and embodiment of the secondhydrolysis catalyst and/or the second mixer correspond to thosedescribed above for the first hydrolysis catalyst and the first mixer.

The exhaust treatment system 350 also comprises a second reductioncatalyst device 332, which is arranged downstream of the second dosagedevice 372. The second reduction catalyst device 332 is arranged toreduce nitrogen oxides NO_(x) in the exhaust stream 303 through use ofthe second additive and, if the first additive remains in the exhauststream 303 when this reaches the second reduction catalyst device 332,also through use of the first additive.

The exhaust treatment system 350 may also be equipped with one orseveral sensors, such as one or several NO_(x)-sensors 361, 363, 364and/or one or several temperature sensors 362, 363, which are arrangedfor the determination of NO_(x)-concentrations and temperatures in theexhaust treatment system 350, respectively. A robustness against errorsin administered doses of reductant may be achieved by way of anembodiment of the invention, wherein an NO_(x)-sensor 363 is placedbetween the two dosage devices 371, 372, and preferably between theparticulate filter 320 and the second dosage device 372, in the exhausttreatment system 350. This makes it possible, by way of the seconddosage device 372, to correct a potential dosage error, which hascreated unforeseen emission levels downstream of the first reductiondevice 371 and/or the particulate filter 320.

This placement of the NO_(x)-sensor 363 between the two dosage devices371, 372 and, preferably, between the particulate filter cDPF 320 andthe second dosage device 372, also makes it possible to correct theamount of additive administered by the second dosage device 372 fornitrogen oxides NO_(x), which may be created over the particulate filtercDPF 320 from excess remainders of additive from the dosage carried outby the first dosage device 371.

The NO_(x)-sensor 364 downstream of the second reduction catalyst device332 may be used at feedback of dosage of additive.

Through the use of the exhaust treatment system 350 shown in FIG. 3,both the first reduction catalyst device 331 and the second reductioncatalyst device 332 may be optimized with respect to a selection ofcatalyst characteristics for the reduction of nitrogen oxides NO_(x),and/or with respect to volumes for the first 331 and second 332reduction catalyst devices, respectively. Through the present invention,the particulate filter 320 is used to the advantage of the function, bytaking into account how its thermal mass impacts the temperature for thesecond reduction catalyst 332, and how the catalytic coating impacts theNO₂/NO_(x)-fraction upstream of the second reduction catalyst 332 atexhaust purification.

By taking into account the thermal inertia of the particulate filter320, the first reduction catalyst device 331 and the second reductioncatalyst device 332, respectively, may be optimized with respect to thespecific temperature function each will experience. Since, according tothe present invention, the optimized first 331 and second 332 reductioncatalyst devices are set up to purify the exhausts in cooperation, theexhaust treatment system 350 may be made compact. Since the spaceallocated to the exhaust treatment system 350, for example in a vehicle,is limited, it is a great advantage to provide a compact exhausttreatment system, through a high usage level of the catalysts usedaccording to the present invention. Such high usage level and theassociated smaller volume requirement, also provide a possibility for areduced back pressure, and accordingly also a lower fuel consumption.

The present invention provides for an exhaust treatment system 350,which efficiently reduces the amount of nitrogen oxides NO_(x) in theexhaust stream in substantially all driving modes, comprising especiallycold starts and throttle, that is to say increased requested torque,from a low exhaust temperature and a load deduction, that is to say froma reduced requested torque. Thus, the exhaust treatment system 350according to the present invention is suitable in substantially alldriving modes, which give rise to a transient temperature evolution inthe exhaust treatment. One example of such a driving mode may consist ofcity driving comprising many starts and decelerations.

The problems with prior art technology, which are related to a too highfraction of nitrogen dioxides NO₂, may be resolved at least partly withthe use of the present invention, since two reduction catalyst devices371, 372 are comprised in the exhaust treatment system 350. The problemmay be resolved by way of combining the present invention with theknowledge that the amount of nitrogen oxides NO_(x) controls how large afraction of nitrogen dioxides NO₂ is obtained downstream of afilter/substrate coated with a catalytic oxidizing coating, that is tosay that the amount of nitrogen oxides NO_(x) may be used to control thevalue of the ratio NO₂/NO_(x). By reducing the nitrogen oxides NO_(x)over the first reduction catalyst device 371 during operation at lowtemperatures, a requirement regarding a given ratio between nitrogendioxide and nitrogen oxides NO₂/NO_(x) in the exhausts reaching thesecond reduction catalyst device 372 may be fulfilled with a smaller,and accordingly less costly, amount of oxidizing coating.

The present invention has an advantage in that the added manufacturingcost as a consequence of the invention may be kept at a low level, sincethe oxidation catalyst DOC 210, available in prior art systems atmanufacture, according to one embodiment of the invention may bereplaced by the first reduction catalyst device 331 according to thepresent invention. Thus, a manufacturing operation, comprising assemblyof the oxidation catalyst DOC 210, may easily be replaced with anothermanufacturing operation, comprising assembly of the first reductioncatalyst device 331 according to the present invention. This results ina minimal added cost to the assembly and/or manufacturing.

Since the oxidation catalyst DOC 210, which was present in prior artsystem, may be replaced with the first reduction catalyst device 331according to the present invention, retrofitting on already manufacturedunits, comprising exhaust treatment systems according to the EuroVI-specification, is possible. Additionally, it is a requirement that anadditional dosage device is fitted in the exhaust treatment system,which comprises devices for mixture and/or vaporization of the additive.

The first reduction catalyst device 331 in the exhaust treatment system350 is, according to one embodiment, active at a lower reductanttemperature interval T_(red) than the oxidation temperature intervalT_(ox), at which the nitrogen dioxide based soot oxidation, that is tosay the oxidation of incompletely oxidized carbon compounds in theparticulate filter 320, is active. In other words, the temperature for aso-called “light-off”for soot oxidation in the particulate filter 320 ishigher than the “light-off” for the reduction of nitrogen oxides NO_(x)in the first reduction catalyst device 331. Accordingly, the reductionof nitrogen oxides NO_(x) in the first reduction catalyst device 331does not necessarily compete with the soot oxidation in the particulatefilter 320, since they are active within at least partly differenttemperature intervals; T_(red)≠T_(ox).

The exhaust treatment system sometimes requests that the engine generateheat for the exhaust treatment system, to be able to achieve asufficient efficiency with respect to exhaust purification. This heatgeneration is then achieved at the expense of the engine's efficiencyrelating to fuel consumption, which decreases. One advantageouscharacteristic of the exhaust treatment system according to the presentinvention, is that the first reduction catalyst device upstream of thefilter may be made to react faster to such generated heat, than whatwould have been possible for example with the Euro VI-system. Therefore,less fuel is consumed overall with the use of the present invention.

According to one embodiment of the present invention, the engine iscontrolled so that it generates such heat in an extent making the firstreduction catalyst device reach a certain given temperature/performance.Therefore, an efficient exhaust purification may be obtained, since thefirst reduction catalyst device may operate at a favorable temperature,while unnecessary heating, and therefore fuel inefficiency, is avoided.

As opposed to the above mentioned prior art solutions, the firstreduction catalyst device 331 according to the present invention doesnot need to be closely connected to the engine and/or the turbo. Thefact that the first reduction catalyst device 331 according to thepresent invention may be fitted further away from the engine and/or theturbo, and for example may be located in the silencer, has an advantagein that a longer mixing distance for additive may be obtained in theexhaust stream between the engine, and/or the turbo, and the firstreduction catalyst device 331. This means that an improved utilizationis obtained for the first reduction catalyst device 331. Meanwhile,thanks to the present invention the many advantages mentioned in thisdocument associated with the potential reduction of nitrogen oxidesNO_(x) both upstream and downstream of the thermally inertial filtercDPF are achieved.

According to different embodiments of the present invention, the firstreduction catalyst device 331 consists of one of:

-   -   a first selective catalytic reduction catalyst SCR₁;    -   a first selective catalytic reduction catalyst SCR₁, integrated        downstream with a first slip-catalyst SC₁, wherein the first        slip-catalyst SC₁ is arranged to oxidize a residue of additive,        wherein the residue may consist for example of urea, ammonia NH₃        or isocyanic acid HNCO, and/or to assist SCR₁ with additional        reduction of nitrogen oxides NO_(x) in the exhaust stream 303;    -   a first selective catalytic reduction catalyst SCR₁, followed        downstream by a separate first slip-catalyst SC₁, wherein the        first slip-catalyst SC₁ is arranged to oxidize a residue of        additive, wherein the residue may consist for example of urea,        ammonia NH₃ or isocyanic acid HNCO, and/or to assist SCR₁ with        further reducing nitrogen oxides NO_(x) in the exhaust stream        303;    -   a first slip-catalyst SC₁, integrated downstream with a first        selective catalytic reduction catalyst SCR₁, wherein the first        slip-catalyst SC₁ is arranged to oxidize additive, and/or to        assist the first selective catalytic reduction catalyst SCR₁        with a reduction of nitrogen oxides NO_(x) in the exhaust stream        303;    -   a first slip-catalyst SC₁, followed downstream by a separate        first selective catalytic reduction catalyst SCR₁, wherein the        first slip-catalyst SC₁ is arranged to oxidize additive, and/or        to assist the first selective catalytic reduction catalyst SCR₁        with a reduction of nitrogen oxides NO_(x) in the exhaust stream        303;    -   a first slip-catalyst SC₁, integrated downstream with a first        selective catalytic reduction catalyst SCR₁, integrated        downstream with an additional first slip-catalyst SC_(1b),        wherein the first slip-catalyst SC₁ and/or the additional first        slip-catalyst SC_(1b) is arranged to oxidize additive, and/or to        assist the first selective catalytic reduction catalyst SCR₁        with a reduction of nitrogen oxides NO_(x) in the exhaust stream        303;    -   a first slip-catalyst SC₁, followed downstream by a separate        first selective catalytic reduction catalyst SCR₁, followed        downstream by a separate additional first slip-catalyst SC_(1b),        wherein the first slip-catalyst SC₁ and/or the additional first        slip-catalyst SC_(1b) is arranged to oxidize additive, and/or to        assist the first selective catalytic reduction catalyst SCR₁        with a reduction of nitrogen oxides NO_(x) in the exhaust stream        303;    -   a first slip-catalyst SC₁, integrated downstream with a first        selective catalytic reduction catalyst SCR₁, followed downstream        by a separate additional first slip-catalyst SC_(1b), wherein        the first slip-catalyst SC₁ and/or the additional first        slip-catalyst SC_(1b) is arranged primarily to reduce nitrogen        oxides NO_(x), and secondarily to oxidize additive in the        exhaust stream 303;    -   a first slip-catalyst SC₁, followed downstream by a separate        first selective catalytic reduction catalyst SCR₁, integrated        downstream with a separate additional first slip-catalyst        SC_(1b), wherein the first slip-catalyst SC₁ and/or the        additional first slip-catalyst SC_(1b) is arranged primarily to        reduce nitrogen oxides NO_(x), and secondarily to oxidize        additive in the exhaust stream 303;    -   a first slip-catalyst SC₁, which is arranged primarily to reduce        nitrogen oxides NO_(x), and secondarily to oxidize a residue of        additive, wherein the residue may consist for example of urea,        ammonia NH₃ or isocyanic acid HNCO, in the exhaust stream 303;        and    -   a first selective catalytic reduction catalyst SCR₁ combined        with an oxidizing coating in the outlet part of the same        substrate, which is also sometimes referred to as “combicat”,        SCR_(komb);    -   a first slip-catalyst SC₁, integrated downstream with a first        selective catalytic reduction catalyst SCR₁ combined with a        purely oxidizing coating in its outlet part on the same        substrate, which is also sometimes referred to as “combicat”,        wherein the first slip-catalyst SC₁ is arranged primarily to        reduce nitrogen oxides NO_(x), and secondarily to oxidize        additive in the exhaust stream 303; and    -   a first slip-catalyst SC₁, followed downstream by a separate        first selective catalytic reduction catalyst SCR₁ combined with        a purely oxidizing coating in its outlet part on the same        substrate, which is also sometimes referred to as “combicat”,        wherein the first slip-catalyst SC₁ is arranged primarily to        reduce nitrogen oxides NO_(x), and secondarily to oxidize        additive in the exhaust stream 303.

According to different embodiments, the second reduction catalyst device332 consists of one of:

-   -   a second selective catalytic reduction catalyst SCR₂;    -   a second selective catalytic reduction catalyst SCR₂, integrated        downstream with a second slip-catalyst SC₂, wherein the second        slip-catalyst SC₂ is arranged to oxidize a residue of additive        and/or to assist SCR₂ with an additional reduction of nitrogen        oxides NO_(x) in the exhaust stream 303; and    -   a second selective catalytic reduction catalyst SCR₂, followed        downstream by a separate second slip-catalyst SC₂, wherein the        second slip-catalyst SC₂ is arranged to oxidize a residue of        additive, and/or to assist SCR₂ with an additional reduction of        nitrogen oxides NO_(x) in the exhaust stream 303.

In this document, the term slip-catalyst SC is used generally to denotea catalyst, which is arranged to oxidize additive in the exhaust stream303, and/or which is arranged so that it is able to reduce residualnitrogen oxides NO_(x) in the exhaust stream 303. According to oneembodiment of the present invention, such a slip catalyst SC is arrangedprimarily to reduce nitrogen oxides NO_(x), and secondarily to oxidize aresidue of additive, that is to say that the slip-catalyst SC is amultifunctional slip-catalyst. In other words, the multifunctionalslip-catalyst SC may take care of slip-residues of both additive andnitrogen oxides NO_(x). This may also be described as the slip-catalystSC being an extended ammonia slip-catalyst ASC, which is set up toreduce nitrogen oxides NO_(x) in the exhaust stream 303, so that ageneral/multifunctional slip-catalyst SC is obtained, which takes careof several types of slip, meaning it takes care of residues of bothadditive and nitrogen oxides NO_(x).

According to one embodiment of the present invention, at least thefollowing reactions may for example be carried out in a multifunctionalslip-catalyst SC, which both reduces nitrogen oxides NO_(x) and oxidizesadditive:

NH₃+O₂→N₂;  (Equation 1)

and

NO_(x)+NH₃→N₂+H₂0.  (Equation 2)

Here, the reaction according to equation 1 results in an oxidation ofadditive, for example residues of additive, comprising ammonia. Thereaction according to equation 2 results in a reduction of nitrogenoxides NO_(x). Accordingly, the additive may here be oxidized, as wellas residues of ammonia NH₃, isocyanic acid HNCO, urea or similar, may beoxidized. These residues of additive, that is to say ammonia NH₃, HNCO,urea or similar, may here also be used to oxidize nitrogen oxidesNO_(x).

In order to obtain these characteristics, that is to say to obtain amultifunctional slip-catalyst, the slip-catalyst may according to oneembodiment comprise one or several substances comprised in platinummetals (PGM; Platinum Group Metals), that is to say one or several ofiridium, osmium, palladium, platinum, rhodium and ruthenium. Theslip-catalyst may also comprise one or several other substances, whichgive the slip-catalyst similar characteristics as platinum group metals.The slip-catalyst may also comprise an NO_(x)-reducing coating, wherethe coating may for example comprise Cu- or Fe-Zeolite or vanadium.Zeolite may here be activated with an active metal, such as for examplecopper (Cu) or iron (Fe).

For both the first 331 and second 332 reduction catalyst device, itscatalytic characteristics may be selected based on the environment towhich it is exposed, or will be exposed to. Additionally, the catalyticcharacteristics for the first 331 and second 332 reduction catalystdevice may be adapted so that they may be allowed to operate insymbiosis with each other. The first 331 and second 332 reductioncatalyst device may also comprise one or several materials, providingthe catalytic characteristic. For example, transition metals such asvanadium and/or tungsten may be used, for example in a catalystcomprising V₂O₅/WO₃/TiO₂. Metals such as iron and/or copper may also becomprised in the first 331 and/or second 332 reduction catalyst device,for example in a Zeolite-based catalyst.

The exhaust treatment system 350, which is schematically illustrated inFIG. 3, may according to different embodiments accordingly have a numberof different structures/configurations, which may be summarized asbelow, and where the respective units SCR₁, SCR₂, cDPF, SCR₁ _(_)_(komb), SC₁, SC_(1b), SC₂ have the respective characteristics describedin this entire document. The particulate filter 320 with the at leastpartly catalytically oxidizing coating is here referred to as cDPF. Thecatalytically oxidizing coating may be adapted according to itscharacteristics, to oxidize nitrogen oxides NO on the one hand, and tooxidize incompletely oxidized carbon compounds on the other.Incompletely oxidized carbon compounds may for example consist of fuelresidue created through the engine's injection system.

According to one configuration according to the invention, the exhausttreatment system has the structure SCR₁-cDPF-SCR₂. That is to say, theexhaust treatment system 350 comprises a first selective catalyticreduction catalyst SCR₁, followed downstream by a particulate filterwith an at least partly catalytically oxidizing coating cDPF, followeddownstream by a second selective catalytic reduction catalyst SCR₂. Asymbiotic usage in the exhaust treatment system 350 of both the firstselectively catalytic reduction catalyst SCR₁, jointly with the secondselectively catalytic reduction catalyst SCR₂ may facilitate theomission of second slip-catalyst SC₂ in the exhaust treatment system 350for certain applications, for example at limited NO_(x)-levels, whichresult in limited conversion level requirements. This is an advantage,for example compared with the above mentioned Euro VI-system, in which aslip-catalyst is, in practice, required. Since an SCR-catalyst istypically cheaper than an SC-catalyst, thanks to this embodiment of theinvention, the manufacturing cost may be reduced by omitting the secondslip-catalyst SC₂.

The first selective catalytic reduction catalyst SCR₁ may be used withthe objective of generating heat, for example by oxidation ofhydrocarbons HC in the exhaust stream, which facilitates regeneration ofsulphur contaminated components, such as the first selective catalyticreduction catalyst SCR₁ and/or components arranged downstream of thelatter. At regeneration of the sulphur contaminated components, theamount of sulphur which is stored in the components is reduced, that isto say in at least one of the first selective catalytic reductioncatalyst SCR₁ and components arranged downstream of the latter.

According to one configuration according to the invention, the exhausttreatment system has the structure SCR₁-SC₁-cDPF-SCR₂. That is to say,the exhaust treatment system 350 comprises a first selective catalyticreduction catalyst SCR₁, followed downstream by a first slip-catalystSC₁, followed downstream by a particulate filter with an at least partlycatalytically oxidizing coating cDPF, followed downstream by a secondselective catalytic reduction catalyst SCR₂. As mentioned above, the useof both the first selectively catalytic reduction catalyst SCR₁ and thesecond selectively catalytic reduction catalyst SCR₂ in the exhausttreatment system 350, facilitates the omission of a second slip-catalystSC₂ in the exhaust treatment system 350 for some applications, whichreduces the manufacturing cost for the vehicle. The use of the firstslip-catalyst SC₁ facilitates a greater load, and therefore a better useof the first selective catalytic reduction catalyst SCR₁, and it alsofacilitates a reduction of the starting temperature (the “lightoff”-temperature) for the NO_(x)-reduction.

According to one embodiment of the present invention, the firstreduction catalyst device 331 here comprises a slip-catalyst SC₁, whichis multifunctional, and therefore reduces nitrogen oxides NO_(x) byusing residues of the additive, and which also oxidizes the residues ofthe additive (as described above). This entails a number of advantagesfor the exhaust treatment system. The first slip-catalyst SC₁ may herebe used in symbiosis with the first reduction catalyst SCR₁, so that theactivity of the first slip-catalyst SC₁ with respect to reduction ofnitrogen oxides NO_(x) and oxidation of residues of additive, as well asthe slip-catalyst's SC₁ deposition characteristics for the reductant,constitute a complement to the function of the first reduction catalystSCR₁. The combination of these characteristics for the first reductioncatalyst device 331, comprising the first reduction catalyst SCR₁ andthe first slip-catalyst SC₁, means that a higher conversion level may beobtained over the first reduction catalyst device 331. In addition, theuse of the first slip-catalyst SC₁ in the first reduction catalystdevice 331 results in conditions making it possible to avoid anon-selective oxidation of reductant occurring in components placeddownstream of the first reduction catalyst device 331 in the exhausttreatment system, which may potentially comprise platinum metals.

Furthermore, tests have shown that the reduction of nitrogen oxidesNO_(x) with the first multifunctional slip-catalyst SC₁ in the firstcatalyst device 331 becomes surprisingly efficient. This is a result ofsufficient amounts of nitrogen oxides NO_(x) being present in theexhaust stream 303 at the first slip-catalyst SC₁ in the first catalystdevice 331, after the first reduction catalyst SCR₁, in order for anefficient reduction of nitrogen oxides NO_(x) to be obtained. In otherwords, the relatively good availability of nitrogen oxides NO_(x) at thefirst slip-catalyst SC₁ may be used to achieve a very good performance,and/or a very good utilization, when a multifunctional slip-catalyst SC₁is used in the first catalyst device 331.

The first selective catalytic reduction catalyst SCR₁, and/or the firstslip-catalyst SC₁, may be used with the objective of generating heat,for example through oxidation of hydrocarbons HC in the exhaust stream,which facilitates regeneration of sulphur contaminated components, suchas the first selective catalytic reduction catalyst SCR₁ and/orcomponents arranged downstream of the latter. At regeneration of thesulphur contaminated components, the amount of sulphur which is storedin the components is reduced, that is to say in at least one of thefirst selective catalytic reduction catalyst SCR₁ and componentsarranged downstream of the latter.

According to one configuration according to the invention, the exhausttreatment system has the structure SCR₁ _(_) _(komb)-cDPF-SCR₂. That isto say, the exhaust treatment system 350 comprises a first selectivecatalytic reduction catalyst SCR₁, combined with an oxidizing coating inthe outlet part on the same substrate (also referred to as “combicat”),followed downstream by a particulate filter with an at least partlycatalytically oxidizing coating cDPF, followed downstream by a secondselective catalytic reduction catalyst SCR₂. Here as well, because ofthe use of both the first selectively catalytic reduction catalyst SCR₁and the second selectively catalytic reduction catalyst SCR₂, the secondslip-catalyst SC₂ may be omitted from the exhaust treatment system 350for certain applications. This exhaust treatment system, that is to saythe system with SCR₁ _(_) _(komb)-cDPF-SCR₂, may facilitate a reductionof the starting temperature (the “light-off”-temperature) for theNO_(x)-reduction, and also has an advantage in that the exhausttemperature may be increased more efficiently in the system, throughoxidation of hydrocarbons in the oxidizing part in the outlet part ofSCR₁ _(_) _(komb). Such a temperature increase may be advantageous at aso-called active regeneration of the particulate filter with the atleast partly catalytically oxidizing coating cDPF.

The first selective catalytic reduction catalyst SCR₁ combined with anoxidizing coating in the outlet part on the same substrate SCR₁ _(_)_(komb), may be used with the objective of generating heat, for examplethrough oxidation of hydrocarbons HC in the exhaust stream, whichfacilitates regeneration of sulphur contaminated components, such as thefirst selective catalytic reduction catalyst SCR₁ combined with anoxidizing coating in the outlet part on the same substrate SCR₁ _(_)_(komb), and/or components arranged downstream of the latter. Atregeneration of the sulphur contaminated components, the amount ofsulphur which is stored in the components is reduced, that is to say inat least one of the first selective catalytic reduction catalyst SCR₁combined with an oxidizing coating in the outlet part on the samesubstrate SCR₁ _(_) _(komb), and components arranged downstream of thelatter.

According to one configuration according to the invention the exhausttreatment system has the structure SCR₁-cDPF-SCR₂-SC₂. That is to say,the exhaust treatment system 350 comprises a first selective catalyticreduction catalyst SCR₁, followed downstream by a particulate filterwith an at least partly catalytically oxidizing coating cDPF, followeddownstream by a second selective catalytic reduction catalyst SCR₂,followed downstream by a second slip-catalyst SC₂. This exhausttreatment system 350 facilitates emission levels for nitrogen oxidesNO_(x) close to zero, since the second reduction catalyst SCR₂ may beheavily loaded, for example by increased dosage of the second additive,since it is followed downstream by the second slip-catalyst SC₂. The useof the second slip-catalyst SC₂ results in additionally improvedperformance for the system, since additional slip may be taken care ofby the second slip-catalyst SC₂.

The first selective catalytic reduction catalyst SCR₁ may be used withthe objective of generating heat, for example by oxidation ofhydrocarbons HC in the exhaust stream, which facilitates regeneration ofsulphur contaminated components, such as the first selective catalyticreduction catalyst SCR₁ and/or components arranged downstream of thelatter. At regeneration of the sulphur contaminated components, theamount of sulphur which is stored in the components is reduced, that isto say in at least one of the first selective catalytic reductioncatalyst SCR₁ and components arranged downstream of the latter

According to one configuration according to the invention, the exhausttreatment system has the structure SCR₁-SC₁-cDPF-SCR₂-SC₂. That is tosay, the exhaust treatment system 350 comprises a first selectivecatalytic reduction catalyst SCR₁, followed downstream by a firstslip-catalyst SC₁, followed downstream by a particulate filter with anat least partly catalytically oxidizing coating cDPF, followeddownstream by a second selective catalytic reduction catalyst SCR₂,followed downstream by a second slip-catalyst SC₂. This exhausttreatment system 350 facilitates emission levels for nitrogen oxidesNO_(x) close to zero, since the second reduction catalyst SCR₂ may bemade to work hard, for example by increased dosage of the secondadditive, since it is followed downstream by the second slip-catalystSC₂. The use of the second slip-catalyst SC₂ results in additionallyimproved performance for the system, since additional slip may be takencare of by the second slip-catalyst SC₂. The use of the firstslip-catalyst SC₁ also facilitates a reduction of the startingtemperature (the “light-off”-temperature) for the NO_(x)-reduction, andmay also result in a greater load and thus an improved utilization ofthe first selective catalytic reduction catalyst SCR₁.

According to one embodiment, the first reduction catalyst device 331here comprises a slip-catalyst SC₁, as described above, which ismultifunctional and therefore reduces nitrogen oxides NO_(x) through theuse of residues of additive, and also oxidizes the residues of theadditive (as described above). This entails a number of advantages forthe exhaust treatment system. The first slip-catalyst SC₁ may here beused in symbiosis with the first reduction catalyst SCR₁, so that theactivity of the first slip-catalyst SC₁ with respect to reduction ofnitrogen oxides NO_(x) and oxidation of residues of additive, as well asthe slip-catalyst's SC₁ deposition characteristics for the reductant,constitute a complement to the function of the first reduction catalystSCR₁. The combination of these characteristics for the first reductioncatalyst device 331, comprising the first reduction catalyst SCR₁ andthe first slip-catalyst SC₁, means that a higher conversion level may beobtained over the first reduction catalyst device 331. In addition, theuse of the first slip-catalyst SC₁ in the first reduction catalystdevice 331 results in conditions making it possible to avoid anon-selective oxidation of reductant occurring in components placeddownstream of the first reduction catalyst device 331 in the exhausttreatment system, which may potentially comprise platinum metals.

Furthermore, tests have shown that the reduction of nitrogen oxidesNO_(x) with the first multifunctional slip-catalyst SC₁ in the firstcatalyst device 331 becomes surprisingly efficient. This is a result ofsufficient amounts of nitrogen oxides NO_(x) being present in theexhaust stream 303 at the first slip-catalyst SC₁ in the first catalystdevice 331, after the first reduction catalyst SCR₁, in order for anefficient reduction of nitrogen oxides NO_(x) to be obtained. In otherwords, the relatively good availability of nitrogen oxides NO_(x) at thefirst slip-catalyst SC₁ is used to achieve a very good performance,and/or a very good utilization, when a multifunctional slip-catalyst SC₁is used in the first catalyst device 331.

The first selective catalytic reduction catalyst SCR₁, and/or the firstslip-catalyst SC₁, may be used with the objective of generating heat,for example by oxidation of hydrocarbons HC in the exhaust stream, whichfacilitates regeneration of sulphur contaminated components, such as thefirst selective catalytic reduction catalyst SCR₁ and/or componentsarranged downstream of the latter. At regeneration of the sulphurcontaminated components, the amount of sulphur which is stored in thecomponents is reduced, that is to say in at least one of the firstselective catalytic reduction catalyst SCR₁ and components arrangeddownstream of the latter.

According to one configuration according to the invention, the exhausttreatment system has the structure SCR₁ _(_) _(komb)-SCR₂-SC₂. That isto say, the exhaust treatment system 350 comprises a first selectivecatalytic reduction catalyst SCR₁, combined with an oxidizing coating inthe outlet part on the same substrate, followed downstream by aparticulate filter with an at least partly catalytically oxidizingcoating cDPF, followed downstream by a second selective catalyticreduction catalyst SCR₂, followed downstream by a second slip-catalystSC₂. This exhaust treatment system 350 also facilitates a reduction ofthe starting temperature (the “light-off”-temperature) for theNO_(x)-reduction, and also has an advantage in that the exhausttemperature may be increased more efficiently in the system throughoxidation of hydrocarbons in the oxidizing part in the outlet part ofSCR₁ _(_) _(komb). Such a temperature increase may be advantageous at aso-called active regeneration of the particulate filter with the atleast partly catalytically oxidizing coating cDPF. This exhausttreatment system 350 also facilitates emission levels for nitrogenoxides NO_(x) close to zero, since the second reduction catalyst SCR₂may be made to work hard, for example by increased dosage of the secondadditive, since it is followed downstream by the second slip-catalystSC₂. The use of the second slip-catalyst SC₂ results in additionallyimproved performance for the system, since additional slip may be takencare of by the second slip-catalyst SC₂. The first selective catalyticreduction catalyst SCR₁ combined with an oxidizing coating in the outletpart on the same substrate SCR₁ _(_) _(komb), may be used with theobjective of generating heat, for example through oxidation ofhydrocarbons HC in the exhaust stream, which facilitates regeneration ofsulphur contaminated components, such as the first selective catalyticreduction catalyst SCR₁ combined with an oxidizing coating in the outletpart on the same substrate SCR₁ _(_) _(komb), and/or components arrangeddownstream of the latter. At regeneration of the sulphur contaminatedcomponents, the amount of sulphur which is stored in the components isreduced, that is to say in at least one of the first selective catalyticreduction catalyst SCR₁ combined with an oxidizing coating in the outletpart on the same substrate SCR₁ _(_) _(komb), and components arrangeddownstream of the latter.

According to one configuration according to the invention, the exhausttreatment system has the structure SC₁-cDPF-SCR₂. That is to say, theexhaust treatment system 350 comprises a first slip-catalyst SC₁,followed downstream by a particulate filter with an at least partlycatalytically oxidizing coating cDPF, followed downstream by a secondselective catalytic reduction catalyst SCR₂. Here as well, because ofthe use of both the first slip-catalyst SC₁ and the second selectivelycatalytic reduction catalyst SCR₂, the second slip-catalyst SC₂ may beomitted from the exhaust treatment system 350 for certain applications.The use of the first slip-catalyst SC₁ facilitates a reduction of thestarting temperature (the “light-off” temperature) for theNO_(x)-reduction.

According to one embodiment of the present invention, the firstreduction catalyst device 331 here comprises only a slip-catalyst SC₁,which is multifunctional and both reduces nitrogen oxides NO_(x) throughthe use of the additive and also oxidizes the additive. This entails anumber of advantages for the exhaust treatment system. Tests have shownthat the reduction of nitrogen oxides NO_(x) with the firstmultifunctional slip-catalyst SC₁ in the first catalyst device 331becomes surprisingly efficient. This is a result of sufficient amountsof nitrogen oxides NO_(x) being present in the exhaust stream 303 at thefirst slip-catalyst SC₁ in the first catalyst device 331, in order foran efficient reduction of nitrogen oxides NO_(x) to be obtained. Inother words, the relatively good availability of nitrogen oxides NO_(x)at the first slip-catalyst SC₁ is used to achieve a very goodperformance, and/or a very good utilization, when a multifunctionalslip-catalyst SC₁ is used in the first catalyst device 331.

The first slip-catalyst SC₁ may be used with the objective of generatingheat, for example by oxidation of hydrocarbons HC in the exhaust stream,which also may facilitate regeneration of sulphur contaminatedcomponents, such as the catalyst and/or components arranged downstreamof the latter. At the regeneration of the sulphur contaminatedcomponents, the amount of sulphur stored in the components is reduced.

According to one configuration according to the invention, the exhausttreatment system has the structure SC₁-cDPF-SCR₂-SC₂. That is to say,the exhaust treatment system 350 comprises a first slip-catalyst SC₁,followed downstream by a particulate filter with an at least partlycatalytically oxidizing coating cDPF, followed downstream by a secondselective catalytic reduction catalyst SCR₂, followed downstream by asecond slip-catalyst SC₂. This exhaust treatment system 350 facilitatesemission levels for nitrogen oxides NO_(x) close to zero, since thesecond reduction catalyst SCR₂ may be made to work hard, that is to saywith a relatively high dosage of the second additive, since it isfollowed downstream by the second slip-catalyst SC₂. The use of thesecond slip-catalyst SC₂ results in additionally improved performancefor the system, since additional slip may be taken care of by the secondslip-catalyst SC₂. The use of the first slip-catalyst SC₁ facilitates areduction of the starting temperature (the “light-off” temperature) forthe NO_(x)-reduction.

According to one embodiment of the present invention, the firstreduction catalyst device 331 here comprises only a slip-catalyst SC₁,which is multifunctional and both reduces nitrogen oxides NO_(x) throughthe use of the additive and also oxidizes the additive (as describedabove). This entails a number of advantages for the exhaust treatmentsystem. Tests have shown that the reduction of nitrogen oxides NO_(x)with the first multifunctional slip-catalyst SC₁ in the first catalystdevice 331 becomes surprisingly efficient. This is a result ofsufficient amounts of nitrogen oxides NO_(x) being present in theexhaust stream 303 at the first slip-catalyst SC₁ in the first catalystdevice 331, in order for an efficient reduction of nitrogen oxidesNO_(x) to be obtained. In other words, the relatively good availabilityof nitrogen oxides NO_(x) at the first slip-catalyst SC₁ is used toachieve a very good performance, and/or a very good utilization, when amultifunctional slip-catalyst SC₁ is used in the first catalyst device331. The first slip-catalyst SC₁ may be used with the objective ofgenerating heat, for example by oxidation of hydrocarbons HC in theexhaust stream, which also facilitates regeneration of sulphurcontaminated components, such as the catalyst and/or components arrangeddownstream of the latter. At the regeneration of the sulphurcontaminated components, the amount of sulphur stored in the componentsis reduced.

According to one configuration according to the invention, the exhausttreatment system has the structure SC₁-SCR₁-cDPF-SCR₂. That is to say,the exhaust treatment system 350 comprises a first slip-catalyst SC₁,followed downstream by a first selective catalytic reduction catalystSCR₁, followed downstream by a particulate filter with an at leastpartly catalytically oxidizing coating cDPF, followed downstream by asecond selective catalytic reduction catalyst SCR₂. As mentioned above,the use of both the first selectively catalytic reduction catalyst SCR₁and the second selectively catalytic reduction catalyst SCR₂ in theexhaust treatment system 350 facilitates the omission of a secondslip-catalyst SC₂ in the exhaust treatment system 350 for someapplications, which reduces the manufacturing cost for the vehicle. Theuse of the first slip-catalyst SC₁ facilitates a greater load, andtherefore a better use of the first selective catalytic reductioncatalyst SCR₁, and also facilitates a reduction of the startingtemperature (the “light off”-temperature) for the NO_(x)-reduction.

According to one embodiment of the present invention, the firstreduction catalyst device 331 comprises a slip-catalyst SC₁, which ismultifunctional and accordingly both reduces nitrogen oxides NO_(x)through the use of the additive, and also oxidizes the additive (asdescribed above), which results in a number of advantages for theexhaust treatment system. The first slip-catalyst SC₁ may here be usedin symbiosis with the first reduction catalyst SCR₁, so that theactivity of the first slip-catalyst SC₁ with respect to reduction ofnitrogen oxides NO_(x) and oxidation of additive, as well as theslip-catalyst's SC₁ deposition characteristics for the reductant,constitute a complement to the function of the first reduction catalystSCR₁. The combination of these characteristics for the first reductioncatalyst device 331, comprising the first reduction catalyst SCR₁ andthe first slip-catalyst SC₁, means that a higher conversion level may beobtained over the first reduction catalyst device 331. In addition, theuse of the first slip-catalyst SC₁ in the first reduction catalystdevice 331 results in conditions making it possible to avoid anon-selective oxidation of reductant occurring in components placeddownstream of the first reduction catalyst device 331 in the exhausttreatment system, which may potentially comprise platinum metals.

Furthermore, tests have shown that the reduction of nitrogen oxidesNO_(x) with the first multifunctional slip-catalyst SC₁ in the firstcatalyst device 331 becomes surprisingly efficient. This is a result ofsufficient amounts of nitrogen oxides NO_(x) being present in theexhaust stream in the first catalyst device 331, at the firstslip-catalyst SC₁ in the first catalyst device 331, in order for anefficient reduction of nitrogen oxides NO_(x) to be obtained. In otherwords, the relatively good availability of nitrogen oxides NO_(x) at thefirst slip-catalyst SC₁ is used to achieve a very good performance,and/or a very good utilization, when a multifunctional slip-catalyst SC₁is used in the first catalyst device 331.

The first selective catalytic reduction catalyst SCR₁, the firstslip-catalyst SC₁, and/or the additional first slip-catalyst SC_(1b),may be used with the objective of generating heat, for example byoxidation of hydrocarbons HC in the exhaust stream, which facilitatesregeneration of sulphur contaminated components, such as the catalystand/or components arranged downstream of the latter. At the regenerationof the sulphur contaminated components, the amount of sulphur stored inthe components is reduced. The use of the first slip-catalyst SC₁upstream of the first selective catalytic reduction catalyst SCR₁results in good possibilities for generating this heat.

According to one configuration according to the invention, the exhausttreatment system has the structure SC₁-SCR₁-cDPF-SCR₂-SC₂. That is tosay, the exhaust treatment system 350 comprises a first slip-catalystSC₁, followed downstream by a first selective catalytic reductioncatalyst SCR₁, followed downstream by a particulate filter with an atleast partly catalytically oxidizing coating cDPF, followed downstreamby a second selective catalytic reduction catalyst SCR₂, followeddownstream by a second slip-catalyst SC₂. This exhaust treatment system350 facilitates emission levels for nitrogen oxides NO_(x) close tozero, since the second reduction catalyst SCR₂ may be made to work hard,for example by increased dosage of the second additive, since it isfollowed downstream by the second slip-catalyst SC₂. The use of thefirst slip-catalyst SC₁ also facilitates a reduction of the startingtemperature (the “light-off”-temperature) for the NO_(x)-reduction, andmay also result in a greater load, and thus an improved utilization ofthe first selective catalytic reduction catalyst SCR₁. The use of thesecond slip-catalyst SC₂ results in additionally improved performancefor the system, since additional slip may be taken care of by the secondslip-catalyst SC₂.

According to one embodiment of the present invention, the firstreduction catalyst device 331 comprises a slip-catalyst SC₁, which ismultifunctional and accordingly both reduces nitrogen oxides NO_(x)through the use of the additive, and also oxidizes the additive (asdescribed above), which results in a number of advantages for theexhaust treatment system. The first slip-catalyst SC₁ may here be usedin symbiosis with the first reduction catalyst SCR₁, so that theactivity of the first slip-catalyst SC₁ with respect to reduction ofnitrogen oxides NO_(x) and oxidation of additive, as well as theslip-catalyst's SC₁ deposition characteristics for the reductant,constitute a complement to the function of the first reduction catalystSCR₁. The combination of these characteristics for the first reductioncatalyst device 331, comprising the first reduction catalyst SCR₁ andthe first slip-catalyst SC₁, means that a higher conversion level may beobtained over the first reduction catalyst device 331. In addition, theuse of the first slip-catalyst SC₁ in the first reduction catalystdevice 331 results in conditions making it possible to avoid anon-selective oxidation of reductant occurring in components placeddownstream of the first reduction catalyst device 331 in the exhausttreatment system, which may potentially comprise platinum metals.

Furthermore, tests have shown that the reduction of nitrogen oxidesNO_(x) with the first multifunctional slip-catalyst SC₁ in the firstcatalyst device 331 becomes surprisingly efficient. This is a result ofsufficient amounts of nitrogen oxides NO_(x) being present in theexhaust stream 303 at the first slip-catalyst SC₁ in the first catalystdevice 331, in order for an efficient reduction of nitrogen oxidesNO_(x) to be obtained. In other words, the relatively good availabilityof nitrogen oxides NO_(x) at the first slip-catalyst SC₁ is used toachieve a very good performance, and/or a very good utilization, when amultifunctional slip-catalyst SC₁ is used in the first catalyst device331.

The first selective catalytic reduction catalyst SCR₁, and/or the firstslip-catalyst SC₁, may be used with the objective of generating heat,for example through oxidation of hydrocarbons HC in the exhaust stream,which facilitates regeneration of sulphur contaminated components, suchas the catalyst and/or components arranged downstream of the latter. Atthe regeneration of the sulphur contaminated components, the amount ofsulphur stored in the components is reduced. The use of the firstslip-catalyst SC₁ upstream of the first selective catalytic reductioncatalyst SCR₁ results in good possibilities for generating this heat.

According to one configuration according to the invention, the exhausttreatment system has the structure SC₁-SCR₁-SC_(1b)-cDPF-SCR₂. That isto say, the exhaust treatment system 350 comprises a first slip-catalystSC₁, followed downstream by a first selective catalytic reductioncatalyst SCR₁, followed downstream by an additional first slip-catalystSC_(1b), followed downstream by a particulate filter with an at leastpartly catalytically oxidizing coating cDPF, followed downstream by asecond selective catalytic reduction catalyst SCR₂. As mentioned above,the use of both the first selectively catalytic reduction catalyst SCR₁and the second selectively catalytic reduction catalyst SCR₂ in theexhaust treatment system 350, facilitates the omission of a secondslip-catalyst SC₂ in the exhaust treatment system 350 for someapplications, which reduces the manufacturing cost for the vehicle. Theuse of the first slip-catalyst SC₁ and the additional firstslip-catalyst SC_(1b) facilitates a greater load, and therefore a betteruse of the first selective catalytic reduction catalyst SCR₁, and alsofacilitates a reduction of the starting temperature (the “lightoff”-temperature) for the NO_(x)-reduction.

According to one embodiment of the present invention, the firstreduction catalyst device 331 here comprises a slip-catalyst SC₁ and anadditional first slip-catalyst SC_(1b), of which at least one ismultifunctional, and accordingly reduces nitrogen oxides NO_(x) throughthe use of the additive, and also oxidizes the additive (as describedabove). This entails a number of advantages for the exhaust treatmentsystem. The first slip-catalyst SC₁ and/or the additional firstslip-catalyst SC_(1b) may here be used in symbiosis with the firstreduction catalyst SCR₁, so that the activity of the first slip-catalystSC₁ and/or the additional first slip-catalyst SC_(1b), with respect tothe reduction of nitrogen oxides NO_(x) and oxidation of additive, aswell as the slip-catalyst's SC₁ and/or the additional firstslip-catalyst SC_(1b) deposit characteristics for reductant, constitutea complement to the function of the first reduction catalyst SCR₁. Thecombination of these characteristics for the first reduction catalystdevice 331, comprising the first reduction catalyst SCR₁, the firstslip-catalyst SC₁, and the additional first slip-catalyst SC_(1b), meansthat a higher conversion level may be obtained over the first reductioncatalyst device 331. Additionally, the use of the first slip-catalystSC₁, and/or the additional first slip-catalyst SC_(1b), in the firstreduction catalyst device 331 result in conditions making it possible toavoid a non-selective oxidation of reductant occurring in componentsplaced downstream of the first reduction catalyst device 331 in theexhaust treatment system, which may potentially comprise platinummetals.

Furthermore, tests have shown that the reduction of nitrogen oxidesNO_(x) with the first multifunctional slip-catalyst SC₁, and/or themultifunctional additional first slip-catalyst SC_(1b), in the firstcatalyst device 331 becomes surprisingly efficient. This is a result ofsufficient amounts of nitrogen oxides NO_(x) being present in theexhaust stream at the first slip-catalyst SC₁, and/or at the additionalfirst slip-catalyst SC_(1b), in the first catalyst device 331, in orderfor an efficient reduction of nitrogen oxides NO_(x) to be obtained. Inother words, the relatively good availability of nitrogen oxides NO_(x)at the first slip-catalyst SC₁, and/or at the additional firstslip-catalyst SC_(1b), may be used to achieve a very good performance,and/or a very good utilization, when a multifunctional slip-catalystSC₁, and/or a multifunctional additional first slip-catalyst SC_(1b) isused in the first catalyst device 331.

The first selective catalytic reduction catalyst SCR₁, the firstslip-catalyst SC₁, and/or the additional first slip-catalyst SC_(1b),may be used with the objective of generating heat, for example byoxidation of hydrocarbons HC in the exhaust stream, which facilitatesregeneration of sulphur contaminated components, such as the catalystand/or components arranged downstream of the latter. At the regenerationof the sulphur contaminated components, the amount of sulphur stored inthe components is reduced. The use of the first slip-catalyst SC₁upstream of the first selective catalytic reduction catalyst SCR₁results in good possibilities for generation this heat.

According to one configuration according to the invention, the exhausttreatment system has the structure SC₁-SCR₁-SC_(1b)-cDPF-SCR₂-SC₂. Thatis to say, the exhaust treatment system 350 comprises a firstslip-catalyst SC₁, followed downstream by a first selective catalyticreduction catalyst SCR₁, followed downstream by an additional firstslip-catalyst SC_(1b), followed downstream by a particulate filter withan at least partly catalytically oxidizing coating cDPF, followeddownstream by a second selective catalytic reduction catalyst SCR₂,followed downstream by a second slip-catalyst SC₂. This exhausttreatment system 350 facilitates emission levels for nitrogen oxidesNO_(x) close to zero, since the second reduction catalyst SCR₂ may bemade to work hard, for example by increased dosage of the secondadditive, since it is followed downstream by the second slip-catalystSC₂. The use of the second slip-catalyst SC₂ results in additionallyimproved performance for the system, since additional slip may be takencare of by the second slip-catalyst SC₂. The use of the firstslip-catalyst SC₁, and the additional first slip-catalyst SC_(1b), alsofacilitates a reduction of the starting temperature (the “lightoff”-temperature) for the NO_(x)-reduction, and may also result in alarger load, and thus in an improved use of the first selectivecatalytic reduction catalyst SCR₁.

According to one embodiment of the present invention the first reductioncatalyst device 331 here comprises a slip-catalyst SC₁, and/or anadditional first slip-catalyst SC_(1b), which is multifunctional, andaccordingly reduces nitrogen oxides NO_(x) through the use of theadditive, and also oxidizes the additive (as described above). Thisentails a number of advantages for the exhaust treatment system. Thefirst slip-catalyst SC₁, and/or the additional first slip-catalystSC_(1b), may here be used in symbiosis with the first reduction catalystSCR₁, so that the activity of the first slip-catalyst SC₁, and/or theadditional first slip-catalyst SC_(1b), with respect to the reduction ofnitrogen oxides NO_(x) and oxidation of additive, as well as theslip-catalyst's SC₁ and/or the additional first slip-catalyst's SC_(1b)deposit characteristics for reductant, constitute a complement to thefunction of the first reduction catalyst SCR₁. The combination of thesecharacteristics for the first reduction catalyst device 331, comprisingthe first reduction catalyst SCR₁, the first slip-catalyst SC₁, and theadditional first slip-catalyst SC_(1b), means that a higher conversionlevel may be obtained over the first reduction catalyst device 331.Additionally, the use of the first slip-catalyst SC₁, and/or of theadditional first slip-catalyst SC_(1b), in the first reduction catalystdevice 331 result in conditions making it possible to avoid anon-selective oxidation of reductant occurring in components placeddownstream of the first reduction catalyst device 331 in the exhausttreatment system, which may potentially comprise platinum metals.

Furthermore, tests have shown that the reduction of nitrogen oxidesNO_(x) with the first multifunctional slip-catalyst SC₁, and/or theadditional first slip-catalyst SC_(1b), in the first catalyst device 331becomes surprisingly efficient. This is a result of sufficient amountsof nitrogen oxides NO_(x) being present in the exhaust stream 303 at thefirst slip-catalyst SC₁, and/or at the additional first slip-catalystSC_(1b), in the first catalyst device 331, in order for an efficientreduction of nitrogen oxides NO_(x) to be obtained. In other words, therelatively good availability of nitrogen oxides NO_(x) at the firstslip-catalyst SC₁, and/or at the additional first slip-catalyst SC_(1b),may be used to achieve a very good performance, and/or a very goodutilization, when a multifunctional slip-catalyst SC₁ and/or amultifunctional additional first slip-catalyst SC_(1b) is used in thefirst catalyst device 331.

The first selective catalytic reduction catalyst SCR₁, the firstslip-catalyst SC₁, and/or the additional first slip-catalyst SC_(1b),may be used with the objective of generating heat, for example byoxidation of hydrocarbons HC in the exhaust stream, which facilitatesregeneration of sulphur contaminated components, such as the catalystand/or components arranged downstream of the latter. At the regenerationof the sulphur contaminated components, the amount of sulphur stored inthe components is reduced. The use of the first slip-catalyst SC₁upstream of the first selective catalytic reduction catalyst SCR₁results in good possibilities for generating this heat.

According to one configuration according to the invention, the exhausttreatment system has the structure SC₁-SCR₁ _(_) _(komb)-cDPF-SCR₂. Thatis to say, the exhaust treatment system 350 comprises a firstslip-catalyst SC₁, followed downstream by a first selective catalyticreduction catalyst, combined with an oxidizing coating in the outletpart on the same substrate SCR₁ _(_) _(komb), followed downstream by aparticulate filter with an at least partly catalytically oxidizingcoating cDPF, followed downstream by a second selective catalyticreduction catalyst SCR₂. As mentioned above, the use of both the firstselectively catalytic reduction catalyst SCR₁ _(_) _(komb), and thesecond selectively catalytic reduction catalyst SCR₂, in the exhausttreatment system 350 facilitates that a second slip-catalyst SC₂ may beomitted from the exhaust treatment system 350 for some applications,which reduces the manufacturing cost for the vehicle. The use of thefirst slip-catalyst SC₁ facilitates a greater load, and thus a betteruse of the first selective catalytic reduction catalyst SCR₁, and alsofacilitates a reduction of the starting temperature (the “lightoff”-temperature) for the NO_(x)-reduction. Additionally, the use of thefirst slip-catalyst SC₁ upstream of the first selective catalyticreduction catalyst SCR₁ combined with an oxidizing coating in the outletpart on the same substrate, provides for a possibility of regenerationof sulphur contaminated components, such as the catalyst and/orcomponents arranged downstream of the latter. At the regeneration of thesulphur contaminated components, the amount of sulphur stored in thecomponents is reduced. Such a regeneration may for example be used whenthe first selective catalytic reduction catalyst combined with anoxidizing coating in the outlet part SCR₁ _(_) _(komb), comprisescopper.

According to one embodiment of the present invention, the firstreduction catalyst device 331 comprises a slip-catalyst SC₁, which ismultifunctional and accordingly both reduces nitrogen oxides NO_(x)through the use of the additive, and also oxidizes the additive (asdescribed above), which results in a number of advantages for theexhaust treatment system. The first slip-catalyst SC₁ may here be usedin symbiosis with the first reduction catalyst SCR₁ _(_) _(komb), sothat the activity of the first slip-catalyst SC₁ with respect toreduction of nitrogen oxides NO_(x) and oxidation of additive, as wellas the slip-catalyst's SC₁ deposit characteristics for reductant,constitutes a complement to the function for the first reductioncatalyst SCR₁ _(_) _(komb). The combination of these characteristics forthe first reduction catalyst device 331, comprising the first reductioncatalyst SCR₁ _(_) _(komb) and the first slip-catalyst SC₁, means that ahigher conversion level may be obtained over the first reductioncatalyst device 331. In addition, the use of the first slip-catalyst SC₁in the first reduction catalyst device 331 results in conditions makingit possible to avoid a non-selective oxidation of reductant occurring incomponents placed downstream of the first reduction catalyst device 331in the exhaust treatment system, which may potentially comprise platinummetals.

Furthermore, tests have shown that the reduction of nitrogen oxidesNO_(x) with the first multifunctional slip-catalyst SC₁ in the firstcatalyst device 331 becomes surprisingly efficient. This is a result ofsufficient amounts of nitrogen oxides NO_(x) being present in theexhaust stream 303 at the first slip-catalyst SC₁ in the first catalystdevice 331, in order for an efficient reduction of nitrogen oxidesNO_(x) to be obtained. In other words, the relatively good availabilityof nitrogen oxides NO_(x) at the first slip-catalyst SC₁ is used toachieve a very good performance, and/or a very good utilization, when amultifunctional slip-catalyst is used in the first catalyst device 331.

The first selective catalytic reduction catalyst combined with anoxidizing coating in the outlet part on the same substrate SCR₁ _(_)_(komb), and/or the first slip-catalyst SC₁, may be used with theobjective of generating heat, for example through oxidation ofhydrocarbons HC in the exhaust stream, which facilitates regeneration ofsulphur contaminated components, such as the catalyst and/or componentsarranged downstream of the latter. At the regeneration of the sulphurcontaminated components, the amount of sulphur stored in the componentsis reduced. The use of the first slip-catalyst SC₁ upstream of the firstselective catalytic reduction catalyst combined with an oxidizingcoating in the outlet part on the same substrate SCR₁ _(_) _(komb),results in good possibilities for generating heat.

According to one configuration according to the invention, the exhausttreatment system has the structure SC₁-SCR₁ _(_) _(komb)-cDPF-SCR₂-SC₂.That is to say, the exhaust treatment system 350 comprises a firstslip-catalyst SC₁, followed downstream by a first selective catalyticreduction catalyst combined with an oxidizing coating in the outlet parton the same substrate SCR₁ _(_) _(komb), followed downstream by aparticulate filter with an at least partly catalytically oxidizingcoating cDPF, followed downstream by a second selective catalyticreduction catalyst SCR₂, followed downstream by a second slip-catalystSC₂. This exhaust treatment system 350 facilitates emission levels fornitrogen oxides NO_(x) close to zero, since the second reductioncatalyst SCR₂ may be made to work hard, for example by increased dosageof the second additive, since it is followed downstream by the secondslip-catalyst SC₂. The use of the second slip-catalyst SC₂ results inadditionally improved performance for the system, since additional slipmay be taken care of by the second slip-catalyst SC₂. The use of thefirst slip-catalyst SC₁ facilitates a greater load, and therefore abetter use of the first selective catalytic reduction catalyst SCR₁, andalso facilitates a reduction of the starting temperature (the “lightoff”-temperature) for the NO_(x)-reduction. Additionally, the use of thefirst slip-catalyst SC₁ upstream of the first selective catalyticreduction catalyst combined with an oxidizing coating in the outlet parton the same substrate SCR₁ _(_) _(komb), provides for a possibility ofregeneration of sulphur contaminated components, such as the catalystand/or components arranged downstream of the latter. At the regenerationof the sulphur contaminated components, the amount of sulphur stored inthe components is reduced. Such a regeneration may for example be used,when the first selective catalytic reduction catalyst combined with anoxidizing coating in the outlet part SCR₁ _(_) _(komb) comprises copper.

According to one embodiment of the present invention, the firstreduction catalyst device 331 comprises a slip-catalyst SC₁, which ismultifunctional and accordingly both reduces nitrogen oxides NO_(x)through the use of the additive, and also oxidizes the additive (asdescribed above), which results in a number of advantages for theexhaust treatment system. The first slip-catalyst SC₁ may here be usedin symbiosis with the first reduction catalyst SCR₁ _(_) _(komb), sothat the activity of the first slip-catalyst SC₁ with respect toreduction of nitrogen oxides NO_(x) and oxidation of additive, as wellas the slip-catalyst's SC₁ deposit characteristics for reductant,constitute a complement to the function for the first reduction catalystSCR₁ _(_) _(komb). The combination of these characteristics for thefirst reduction catalyst device 331, comprising the first reductioncatalyst SCR₁ _(_) _(komb) and the first slip-catalyst SC₁, means that ahigher conversion level may be obtained over the first reductioncatalyst device 331. In addition, the use of the first slip-catalyst SC₁in the first reduction catalyst device 331 results in conditions makingit possible to avoid a non-selective oxidation of reductant occurring incomponents placed downstream of the first reduction catalyst device 331in the exhaust treatment system, which may potentially comprise platinummetals.

Furthermore, tests have shown that the reduction of nitrogen oxidesNO_(x) with the first multifunctional slip-catalyst SC₁ in the firstcatalyst device 331 becomes surprisingly efficient. This is a result ofsufficient amounts of nitrogen oxides NO_(x) being present in theexhaust stream 303 at the first slip-catalyst SC₁ in the first catalystdevice 331, in order for an efficient reduction of nitrogen oxidesNO_(x) to be obtained. In other words, the relatively good availabilityof nitrogen oxides NO_(x) at the first slip-catalyst SC₁ is used toachieve a very good performance, and/or a very good utilization, when amultifunctional slip-catalyst is used in the first catalyst device 331.

The first selective catalytic reduction catalyst combined with anoxidizing coating in the outlet part on the same substrate SCR₁ _(_)_(komb), and/or the first slip-catalyst SC₁, may be used with theobjective of generating heat, for example through oxidation ofhydrocarbons HC in the exhaust stream, which facilitates regeneration ofsulphur contaminated components, such as the catalyst and/or componentsarranged downstream of the latter. At the regeneration of the sulphurcontaminated components, the amount of sulphur stored in the componentsis reduced. The use of the first slip-catalyst SC₁ upstream of the firstselective catalytic reduction catalyst combined with an oxidizingcoating in the outlet part on the same substrate SCR₁ _(_) _(komb),results in good possibilities for generating heat.

In the configurations listed above according to the embodiments, asdescribed above, the first reduction catalyst SCR₁/SCR₁ _(_) _(komb) andthe first slip-catalyst SC₁ may consist of an integrated unit,comprising both SCR₁/SCR₁ _(_) _(komb) and SC₁, or may consist ofseparate units for SCR₁/SCR₁ _(_) _(komb) and SC₁.

In the configurations listed above according to the embodiments, asdescribed above, the first reduction catalyst SCR₁, the firstslip-catalyst SC₁, and the additional first slip-catalyst SC_(1b), maycomprise an integrated unit comprising two or all of SCR₁, SC₁ andSC_(1b), or may consist of separate units for SCR₁, SC₁ and SC_(1b).

Similarly, the first reduction catalyst device 331 and the particulatefilter cDPF may consist of an integrated unit, comprising both the firstreduction catalyst device 331 and the particulate filter cDPF, or mayconsist of separate units for the first reduction catalyst device 331and the filter cDPF.

Similarly, the second reduction catalyst SCR₂ and the secondslip-catalyst SC₂ may either consist of an integrated unit, comprisingboth SCR₂ and SC₂, or may consist of separate units for SCR₂ and SC₂.

Similarly, the first slip-catalyst SC₁ and cDPF 320 may constitute atleast partly integrated units, or comprise separate units.

According to one embodiment of the present invention, the exhausttreatment system 350 comprises a system 370 for supply of additive,which comprises at least one pump 373 arranged to supply the first 371and the second 372 dosage devices with additive, that is to say, forexample, ammonia or urea.

The system 370 supplies, according to one embodiment, at least one ofthe first 371 and the second 372 dosage devices with additive in liquidform. Additive in liquid form may be filled up at many fillingstations/petrol stations where fuel is provided, so that the additivemay be refilled, and accordingly an optimized use of the two reductionsteps in the exhaust treatment system may be ensured, wherein theoptimized use may, for example, entail that both the first and thesecond dosage device may be used for dosage at different types ofoperation. The optimized use is then, for example, not limited to thefirst dosage device being used only at cold starts. Today, there arethus already existing distribution networks for liquid additives,ensuring availability of additive where the vehicle is driven.

Additionally, the vehicle needs only to be completed with an additionaldosage device, the first 371 dosage device, if only liquid additive isavailable for use. Accordingly, added complexity is minimized throughthe use of only liquid additive. If, for example, gaseous additive isalso used, in addition to the liquid additive, the exhaust treatmentsystem needs to be used with a complete system for supply of the gaseousadditive. In addition, a distribution network and/or logistics forsupply of the gaseous additive needs to be built.

The total exhaust treatment system's secondary emission of, for example,ammonia NH₃, nitrogen dioxides NO₂, and/or laughing gas N₂O at ordinaryoperation of the combustion engine, that is to say not only at coldstarts, may through the use of one embodiment of the present inventionbe reduced, by way of the additive being administered at both the first371 and the second 372 dosage device. This presumes, however, that it ispossible to provide a substantially continuous dosage at the use of theembodiment. By using additive in liquid form, the additive lasts longerwithout interruption for service, since additive in liquid form isavailable for purchase at ordinary petrol stations. Accordingly,substantially continuous dosage with both the first 371 and the second372 dosage device may be made during the entire normal service intervalsfor a vehicle.

The possibility of continuous dosage with both the first 371 and second372 dosage device means that the exhaust treatment system may be used toits full potential. Thus, the system may be controlled, so that robustand very high total levels of NO_(x)-conversion may be obtained overtime, without the system having to compensate for running out ofadditive. The secured availability of additive also means that areliable control of the NO₂-level NO₂/NO_(x) may always be carried out,that is to say during the entire service interval.

Using additive in liquid form for dosage with both the first 371 and thesecond 372 dosage device, means that the complexity of the system 370 iskept low, since a joint tank may be used for storage of the additive.Additive in liquid form may be filled up at many filling stations/petrolstations where fuel is provided, so that the additive may be refilled,and accordingly an optimized use of the two reduction steps in theexhaust treatment system may be ensured.

According to another embodiment, the system 370 supplies at least one ofthe first 371 and the second 372 dosage devices with additive in gaseousform. According to one embodiment this additive may consist of hydrogenH₂.

One example of such a system 370 for supply of additive is shownschematically in FIG. 3, where the system comprises the first dosagedevice 371 and the second dosage device 372, which are arranged upstreamof the first reduction catalyst 331, and upstream of the secondreduction catalyst 332, respectively. The first and second dosagedevices 371, 372, often consisting of dosage nozzles which administeradditive to, and mix such additive with, the exhaust stream 303, aresupplied with additive by the at least one pump 373, via conduits 375for additive. The at least one pump 373 obtains additive from one orseveral tanks 376 for additive, via one or several conduits 377 betweenthe tank/tanks 376, and the at least one pump 373. It should be realizedhere that the additive may be in liquid form and/or gaseous form, asdescribed above. Where the additive is in liquid form, the pump 373 is aliquid pump and the one or several tanks 376 are liquid tanks. Where theadditive is in gaseous form, the pump 373 is a gas pump, and the one orseveral tanks 376 are gas tanks. If both gaseous and liquid additivesare used, several tanks and pumps are arranged, wherein at least onetank and one pump are set up to supply liquid additive, and at least onetank and one pump are set up to supply gaseous additive.

According to one embodiment of the invention, the at least one pump 373comprises a joint pump, which feeds both the first 371 and the second372 dosage device with the first and the second additive, respectively.According to another embodiment of the invention, the at least one pumpcomprises a first and a second pump, which feed the first 371 and thesecond 372 dosage device, respectively, with the first and the secondadditive, respectively. The specific function of the additive system 370is well described in prior art technology, and the exact method for theinjection of additive is therefore not described in any further detailherein. Generally, however, the temperature at the point ofinjection/SCR-catalyst should be above a lower threshold temperature toavoid precipitates and formation of unwanted by-products, such asammonium nitrate NH₄NO₃. An example of a value for such a lowerthreshold temperature may be approximately 200° C. According to oneembodiment of the invention, the system 370 for supply of additivecomprises a dosage control device 374, arranged to control the at leastone pump 373, so that the additive is supplied to the exhaust stream.The dosage control device 374 comprises, according to one embodiment, afirst pump control device 378 arranged to control the at least one pump373, in such a manner that a first dosage of the first additive issupplied to the exhaust stream 303, via the first dosage device 371. Thedosage control device 374 also comprises a second pump control device379, arranged to control the at least one pump 373, so that a seconddosage of the second additive is supplied to the exhaust stream 303, viathe second dosage device 372.

The first and second additives usually consist of the same type ofadditive, for example urea. However, according to one embodiment of thepresent invention, the first additive and the second additive may be ofdifferent types, for example urea and ammonia, which means that thedosage to each one of the first 331 and second 332 reduction catalystdevices, and accordingly also the function for each of the first 331 andsecond 332 reduction catalyst devices, may be optimized also withrespect to the type of additive. If different types of additive areused, the tank 376 comprises several sub-tanks, which contain thedifferent respective types of additive. One or several pumps 373 may beused to supply the different types of additive to the first dosagedevice 371 and the second dosage device 372. As mentioned above, the oneor several tanks, and the one or several pumps, are adapted according tothe state of the additive, that is to say according to whether theadditive is gaseous or liquid.

The one or several pumps 373 are thus controlled by a dosage controldevice 374, which generates control signals for the control of supply ofadditive, so that a desired amount is injected into the exhaust stream303 with the help of the first 371 and the second 372 dosage device,respectively, upstream of the first 331 and the second 332 reductioncatalyst device, respectively. In more detail, the first pump controldevice 378 is arranged to control either a joint pump, or a pumpdedicated to the first dosage device 371, so that the first dosage iscontrolled to be supplied to the exhaust stream 303 via the first dosagedevice 371. The second pump control device 379 is arranged to controleither a joint pump, or a pump dedicated to the second dosage device372, so that the second dosage is controlled to be supplied to theexhaust stream 303 via the second dosage device 372.

According to one aspect of the present invention, a method is providedfor the treatment of an exhaust stream 303, which is emitted by acombustion engine 301. This method is described herein with the help ofFIG. 4, in which the method steps follow the flow of the exhaust streamthrough the exhaust treatment system 350.

In a first step 401 of the method, the exhaust stream is supplied with afirst additive with the use of a first dosage device 371. In a secondstep 402 of the method, a reduction of nitrogen oxides NO_(x) is carriedout in the exhaust stream with the use of this first additive, in afirst reduction catalyst device 331, which may comprise a firstselective catalytic reduction catalyst SCR₁, and/or a firstslip-catalyst SC₁, and/or the above described SCR₁ _(_) _(komb), and/orthe additional first slip-catalyst SC_(1b), arranged downstream of thefirst dosage device 371. The first slip-catalyst SC₁, and/or theadditional first slip-catalyst SC_(1b), here oxidises a residue of theadditive, wherein such residue may consist for example of urea, ammoniaNH₃, or isocyanic acid HNCO, and/or provides an additional reduction ofnitrogen oxides NO_(x) in the exhaust stream 303. It should be notedthat the reduction of nitrogen oxides NO_(x) with the first reductioncatalyst device 331 in this document may comprise partial oxidation, aslong as the total reaction constitutes a reduction of nitrogen oxidesNO_(x).

In a third step 403 of the method, the exhaust stream is filtered, sothat soot particles are caught up by a particulate filter 320, which atleast partly comprises a catalytically oxidizing coating. Thiscatalytically oxidizing coating oxidizes the caught soot particles, andone or several incompletely oxidized nitrogen and/or carbon compounds.

In a fourth step 404 of the method, a second additive is supplied to theexhaust stream 303 with the use of a second dosage device 372. In afifth step 405 of the method, a reduction of the nitrogen oxides NO_(x)in the exhaust stream 303 is carried out, through the use of at leastthe second additive in a second reduction catalyst device 332, which maycomprise a second selective catalytic reduction catalyst SCR₂, and insome configurations a second slip-catalyst SC₂, arranged downstream ofthe second dosage device 371. The second slip-catalyst here oxidizes asurplus of ammonia, and/or provides an additional reduction of nitrogenoxides NO_(x) in the exhaust stream 303. It should be noted that thereduction of nitrogen oxides NO_(x) with the second reduction catalystdevice 332 in this document may comprise partial oxidation, as long asthe total reaction constitutes a reduction of nitrogen oxides NO_(x).

It may be noted that a first temperature T1, which the first reductioncatalyst device 331 is exposed to, and a second temperature T2, whichthe second reduction catalyst device 332 is exposed to, is verysignificant to the function of the exhaust treatment system 350.However, it is difficult to control these temperatures T1, T2, sincethey to a great extent depend on how the driver drives the vehicle, thatis to say that the first T1 and second T2 temperatures depend on thecurrent operation of the vehicle, and inputs via, for example, theaccelerator pedal in the vehicle.

The method for exhaust treatment, and the exhaust treatment system 350itself, become considerably more efficient than a traditional system (asshown in FIG. 2) by way of the first temperature T1 for the firstreduction catalyst device 331 reaching, at for example startingprocesses, higher values for the first temperature T1 faster, andtherefore achieving a higher efficiency at the reduction of nitrogenoxides NO_(x), through the method according to the present invention.Accordingly, a more efficient reduction of nitrogen oxides NO_(x) isobtained, for example at cold starts and throttle from low exhausttemperatures, resulting in a smaller increase of fuel consumption insuch driving modes. In other words, the present invention utilizes thefirst T1 and second T2 temperatures, which are difficult to control, toits advantage, so that they contribute to increasing the overallefficiency of the exhaust purification system.

The above mentioned advantages for the exhaust treatment system 350 arealso obtained for the method according to the present invention.

As mentioned above, according to one embodiment of the presentinvention, the slip-catalyst SC₁, SC₂ may be a multifunctionalslip-catalyst, which both reduces nitrogen oxides NO_(x), and oxidizesresidues of additive, for example by way of primarily reducing nitrogenoxides NO_(x), and secondarily oxidizing residues of additive. In orderto obtain these characteristics, the slip-catalyst may, according to oneembodiment, comprise one or several substances comprised in platinummetals, and/or one or several other substances that provide theslip-catalyst with similar characteristics as for the platinum metalgroup.

Such a multifunctional slip-catalyst SC₁, comprised in the firstreduction catalyst device 331, may according to one embodiment of theinvention constitute the first reduction catalyst device 331 on its own,meaning that the first reduction catalyst device 331 consists only ofthe multifunctional slip-catalyst SC₁.

Such a multifunctional slip-catalyst SC₁, SC_(1b), comprised in thefirst reduction catalyst device 331, may, according to anotherembodiment of the invention, constitute the first reduction catalystdevice 331 in combination with a first reduction catalyst SCR₁, meaningthat the first reduction catalyst device 331 consists of the firstreduction catalyst SCR₁, and the multifunctional slip-catalyst SC₁, andaccording to some embodiments also of an additional first slip-catalystSC_(1b).

Such a multifunctional slip-catalyst SC₁, SC_(1b), comprised in thefirst reduction catalyst device 331, may, according to one embodiment ofa method according to the invention, be used in a novel way in relationto prior art uses of slip-catalysts.

This new method for use of the multifunction slip-catalyst SC₁, SC_(1b)uses the fact that the exhaust stream 303, when it passes through thefirst slip-catalyst SC₁, and/or the additional first slip-catalystSC_(1b), placed in the first reduction catalyst device 331, is rich innitrogen oxides NO_(x), that is to say, it contains a relatively largefraction of nitrogen oxides NO_(x), meaning that the exhaust streamcontains a surplus of NO_(x)-content in relation to the NH₃-content.This relatively large fraction of nitrogen oxides NO_(x), that is to saythe surplus of NO_(x) in relation to NH₃, at the first reductioncatalyst device 331 by far exceeds the fraction of nitrogen oxidesNO_(x), that is to say the surplus of NO_(x) in relation to NH₃ in theexhaust stream 303 when this passes the second reduction catalyst device332, which means that the first slip-catalyst SC₁, and/or the additionalfirst slip-catalyst SC_(1b), in the first reduction catalyst device 331has a totally different impact on the exhaust stream 303 compared to asecond slip-catalyst SC₂ in the second reduction catalyst device 332.This is due to the fact that the exhaust stream 303 contains much lessof a surplus of nitrogen oxides NO_(x), that is to say a much smallersurplus of NO_(x) in relation to NH₃, at the second reduction catalystdevice 332, than at the first reduction catalyst device 331.

When the first slip-catalyst SC₁, and/or the additional firstslip-catalyst SC_(1b), in the first reduction catalyst device 331 hasgood access to nitrogen oxides NO_(x), that is to say when it has arelatively large surplus of NO_(x) in relation to NH₃, it may thus beused as a multifunctional slip-catalyst both for reduction of nitrogenoxides NO_(x) and for oxidation of additive, such as for exampleresidues of additive having passed through a first reduction catalystSCR₁.

For the second slip-catalyst SC₂ in the second reduction catalyst device332, substantially only oxidation of residues of additive having passedthrough the second reduction catalyst SCR₂ is obtained, since only lowlevels of nitrogen oxides NO_(x) are available in the exhaust stream303.

The multifunctional first slip-catalyst SC₁, and/or the additional firstslip-catalyst SC_(1b) 700, according to one embodiment comprises atleast two active layers/strata arranged on at least one stabilizinglayer/stratum 701, which is schematically illustrated in FIG. 7. Itshould be noted that the embodiment shown in FIG. 7 only is an exampleof a possible design of a multifunctional first slip-catalyst SC₁,and/or an additional first slip-catalyst SC_(1b). A multifunctionalfirst slip-catalyst SC₁, and/or an additional first slip-catalystSC_(1b), may be adapted in a number of other ways, as long as the abovedescribed reactions, which may for example correspond to equations 1 and2, are achieved by the multifunctional first slip-catalyst SC₁, and/orthe additional first slip-catalyst SC_(1b). Accordingly, a number ofdesigns, apart from the one shown in FIG. 7, of the multifunctionalfirst slip-catalyst SC₁, and/or the additional first slip-catalystSC_(1b), which result in an oxidation of additive and a reduction ofnitrogen oxides NO_(x), may be used for the multifunctional firstslip-catalyst SC₁, and/or the additional first slip-catalyst SC_(1b).

The first layer 702 of these active layers comprises one or severalsubstances, comprised in the platinum metals, or one or several othersubstances, which provide the slip-catalyst with similar characteristicsas does the platinum metal group, that is to say, for example, oxidationof ammonia. The second layer 703 may comprise an NO_(x)-reducingcoating, for example comprising Cu- or Fe-Zeolite, or vanadium. Zeoliteis here activated with an active metal, such as for example copper (Cu)or iron (Fe). The second layer 703 is here in direct contact with theexhaust stream 303 that passes through the exhaust treatment system.

The multifunctional first slip-catalyst SC₁, and/or the additional firstslip-catalyst SC_(1b), according to one embodiment of the presentinvention, are of a relatively small size, so that a space velocity ofover approximately 50,000 per hour may be obtained for a majority ofdriving modes. The use of the size-limited first slip-catalyst SC₁,and/or the additional first slip-catalyst SC_(1b), in the firstreduction catalyst device 331, wherein there is good access to nitrogenoxides NO_(x) in relation to the access to ammonia, but wherein thereare limitations in relation to the volume/size of the slip-catalyst SC₁,SC_(1b), results in several surprising advantages.

First, the first slip-catalyst SC₁, and/or the additional firstslip-catalyst SC_(1b), may thus be used here as a multifunctionalslip-catalyst, both for reduction of nitrogen oxides NO_(x) and foroxidation of additive. The excellent availability of nitrogen oxidesNO_(x) at the first slip-catalyst SC₁, and/or at the additional firstslip-catalyst SC_(1b), results in a very efficient, good reduction ofnitrogen oxides NO_(x) with the first slip-catalyst SC₁, and/or at theadditional first slip-catalyst SC_(1b).

Additionally, tests have shown that the brief dwell-time of the exhauststream 303 at the first slip-catalyst SC₁, and/or at the additionalfirst slip-catalyst SC_(1b), which is due to the fact that, because ofits relatively limited size, the exhaust stream flows past the firstslip-catalyst SC₁, and/or the additional first slip-catalyst SC_(1b),quickly, in combination with the very good availability of nitrogenoxides NO_(x), results in a very selective multifunctional slip-catalystSC₁, SC_(1b). It has been shown that the first slip-catalyst SC₁, and/orthe additional first slip-catalyst SC_(1b), are used surprisinglyintensely under these conditions, that is to say at a brief dwell-timeand with a high fraction of nitrogen oxides NO_(x), which results in avery good reduction of nitrogen oxides NO_(x).

In other words, the ability of the first slip-catalyst SC₁, and/or theadditional first slip-catalyst SC_(1b), to contribute with a reductionof the nitrogen oxides NO_(x), and/or with oxidation of for examplehydrocarbons and/or ammonia NH₃, may be impacted through selection of asuitable size for the first slip-catalyst SC₁ and/or the additionalfirst slip-catalyst SC_(1b), and/or by adding a suitable exhaustcomposition, for example containing suitable fractions of NO_(x) and/orNH₃.

According to one embodiment of the present invention, the firstreduction catalyst device 331, that is to say the first slip-catalystSC₁, the first reduction catalyst SCR₁, and/or the additional firstslip-catalyst SC_(1b), may be used for oxidation of hydrocarbons HCand/or carbon monoxide CO, which occur naturally in the exhaust stream.For example, hydrocarbons HC in the exhaust stream 303 may be comprisedin fuel residues from the combustion in the combustion engine 101,and/or from extra injections of fuel in connection with regeneration ofthe particulate filter cDPF.

The oxidation of hydrocarbons HC in the first reduction catalyst device331 may also comprise at least one exothermal reaction, that is to say areaction which generates heat, so that a temperature increase ensues forthe first reduction catalyst device 331, and/or for components followingdownstream, such as the particulate filter cDPF 320 and/or a silencer,in the exhaust treatment system 350. Such temperature increase may beused at soot oxidation in the particulate filter cDPF 320, and/or toclean the silencer of by-products, such as for example urea. Throughthis at least one exothermal reaction, oxidation of hydrocarbons HC isalso facilitated in the first reduction catalyst device 331.Additionally, the SCR-layer in the first slip-catalyst SC₁, and/or theadditional first slip-catalyst SC_(1b), may be deactivated over time byfor example sulphur, which means that a heat generating exothermalreaction may be needed in order to secure the function of the firstslip-catalyst SC₁, and/or the additional first slip-catalyst SC_(1b),through a regeneration. Similarly, a heat generating exothermal reactionmay be used in order to secure, through a regeneration, the function ofa first selective reduction catalyst SCR₁. As mentioned above, theregeneration reduces the amount of sulphur in the catalyst/componentwhich is regenerated.

The first multifunctional slip-catalyst SC₁, and/or the additional firstslip-catalyst SC_(1b), placed in the first reduction catalyst device331, also has an ability to oxidize nitrogen monoxide NO into nitrogendioxide NO₂. Thus, nitrogen dioxide NO₂ is supplied to the particulatefilter cDPF placed downstream, which facilitates an efficient sootoxidation in the particulate filter cDPF, where soot oxidation is anitrogen dioxide based oxidation.

Availability of nitrogen dioxide NO₂ downstream of the firstmultifunctional slip-catalyst SC₁, and/or the additional firstslip-catalyst SC_(1b), also means that an increased reduction ofnitrogen oxides NO_(x) over the second reduction catalyst device 332 maybe obtained.

According to one embodiment of the present invention, the firstmultifunctional slip-catalyst SC₁, and/or the multifunctional additionalfirst slip-catalyst SC_(1b), comprises one or several suitablesubstances, such as the above mentioned platinum metals, which createthe at least one exothermal reaction, which results in the temperatureincrease when the one or several suitable substances react with theexhaust stream 303. At the reactions, nitrogen monoxide NO is oxidizedinto nitrogen dioxide NO₂. At the reactions, carbon monoxide NO, and/orhydrocarbons HC, are oxidized as described above.

The characteristics listed above and the advantages specified for afirst multifunctional slip-catalyst SC₁, and/or the additional firstslip-catalyst SC_(1b) in the first reduction catalyst device 331, may bemade to function very well for an exhaust treatment system 350 asdescribed above, that is to say with a first reduction catalyst device331, followed downstream by a particulate filter, partly coated with acatalytic coating cDPF 320, followed downstream by a second reductioncatalyst device 332, and without any oxidation catalyst DOC between thefirst reduction catalyst device 331 and the filter cDPF 320.

According to one embodiment of the method according to the presentinvention, the reduction is controlled with the first reduction catalystdevice 331, so that it occurs within a reduction temperature intervalT_(red), which at least partly differs from an oxidation temperatureinterval T_(ox), within which a significant soot oxidation in theparticulate filter 320 occurs, T_(red)≠T_(ox), so that the reduction ofnitrogen oxides NO_(x) in the first reduction catalyst device does notcompete significantly with the nitrogen dioxide based soot oxidation inthe particulate filter cDPF.

According to one embodiment of the method according to the presentinvention, the supply of additive to the first dosage device 371, and/orthe second dosage device 372, is increased to a level of suppliedadditive at which residues/precipitates/crystallisation may arise. Thislevel may for example be determined by way of a comparison with apredetermined threshold value for the supply. The use of this embodimentmay thus result in residues/precipitates/crystals of additive beingcreated.

According to one embodiment of the method according to the presentinvention, the supply of additive to the first dosage device 371, and/orthe second dosage device 372, is reduced when precipitates/residues ofadditive have formed, so that these precipitates may be heated away. Thereduction may entail that the supply is cut completely. Accordingly, forexample a larger dosage amount in the first dosage position for thefirst reduction catalyst device may be allowed, since potentialprecipitates/residues may be heated away naturally, at the same time asthe emission requirements are met by the second reduction catalystdevice during this time. The reduction/interruption of supply may heredepend on currently measured and/or predicted operating conditions forthe combustion engine, and/or the exhaust treatment system. Thus, forexample, the second reduction catalyst device 332 does not have to beset up to cope with an interruption of the supply through the firstdosage device 371 for all operating modes. An intelligent controltherefore facilitates a smaller system, which may be used when suitable,and when this system may provide a required catalytic function.

According to one embodiment of the method, the first reduction catalystdevice 371 is optimized based on characteristics, such as catalyticcharacteristics, for the first 371, and/or the second 372 reductioncatalyst device. Additionally, the second reduction catalyst device 372may be optimized based on characteristics, such as catalyticcharacteristics, for the first 371, and/or the second 372 reductioncatalyst device. These possibilities of optimizing the first reductioncatalyst device, and/or the second reduction catalyst device, result inan overall efficient exhaust purification, which better reflects theconditions of the complete exhaust treatment system.

The above mentioned characteristics for the first 371, and/or second 372reduction catalyst device, may be related to one or several catalyticcharacteristics for the first 371 and/or the second 372 reductioncatalyst device, a catalyst type for the first 371 and/or the second 372reduction catalyst device, a temperature interval, within which thefirst 371 and/or the second 372 reduction catalyst device is active, anda coverage of ammonia for the first 371 and/or the second 372 reductioncatalyst device 372.

According to one embodiment of the present invention, the firstreduction catalyst device 371 and the second reduction catalyst device372, respectively, are optimized based on operating conditions for thefirst 371 and the second 372 reduction catalyst device, respectively.These operating conditions may be related to a temperature, that is tosay a static temperature, for the first 371 and the second 372 reductioncatalyst device, respectively, and/or to a temperature trend, that is tosay to a change of the temperature, for the first 371 and the second 372reduction catalyst device, respectively.

According to one embodiment of the method according to the presentinvention, an active control is implemented of the reduction carried outby the first reduction catalyst device 331, based on a relationshipbetween the amount of nitrogen dioxide NO₂ _(_) ₂ and the amount ofnitrogen oxides NO_(x) _(_) ₂ reaching the second reduction catalystdevice 332. In other words, the ratio NO₂ _(_) ₂/NO_(x) _(_) ₂ iscontrolled, so that it has a suitable value for the reduction in thesecond reduction catalyst device 332, through which a more efficientreduction may be obtained. In further detail, herein the first reductioncatalyst device 331 has a first reduction of a first amount of nitrogenoxides NO_(x) _(_) ₁ reaching the first reduction catalyst device 331.At the second reduction catalyst device 332, a second reduction of asecond amount of nitrogen oxides NO_(x) _(_) ₂ reaching the secondreduction catalyst device 332, is carried out, wherein an adaptation iscarried out of the ratio NO₂ _(_) ₂/NO_(x) _(_) ₂, between the amount ofnitrogen dioxide NO₂ _(_) ₂ and the second amount of nitrogen oxidesNO_(x) _(_) ₂ reaching the second reduction catalyst device 332. Thisadaptation is carried out herein with the use of an active control ofthe first reduction, based on a value for the ratio NO₂ _(_) ₂/NO_(x)_(_) ₂ with the intention of providing the ratio NO₂ _(_) ₂/NO_(x) _(_)₂ with a value making the second reduction more efficient. The value forthe ratio NO₂ _(_) ₂/NO_(x) _(_) ₂ may herein consist of a measuredvalue, a modelled value and/or a predicted value.

A person skilled in the art will realize that a method for treatment ofan exhaust stream according to the present invention may also beimplemented in a computer program, which when executed in a computerwill cause the computer to execute the method. The computer programusually forms a part of a computer program product 503, wherein thecomputer program product comprises a suitable digitalnon-volatile/permanent/persistent/durable storage medium on which thecomputer program is stored. Saidnon-volatile/permanent/persistent/durable computer readable mediumconsists of a suitable memory, e.g.: ROM (Read-Only Memory), PROM(Programmable Read-Only Memory), EPROM (Erasable PROM), Flash, EEPROM(Electrically Erasable PROM), a hard disk device, etc.

FIG. 5 schematically shows a control device 500. The control device 500comprises a calculation unit 501, which may consist of essentially asuitable type of processor or microcomputer, e.g. a circuit for digitalsignal processing (Digital Signal Processor, DSP), or a circuit with apredetermined specific function (Application Specific IntegratedCircuit, ASIC). The calculation unit 501 is connected to a memory unit502, installed in the control device 500, providing the calculationdevice 501 with e.g. the stored program code and/or the stored data,which the calculation device 501 needs in order to be able to carry outcalculations. The calculation unit 501 is also set up to store interimor final results of calculations in the memory unit 502.

Further, the control device 500 is equipped with devices 511, 512, 513,514 for receiving and sending of input and output signals, respectively.These input and output signals may contain wave shapes, pulses, or otherattributes, which may be detected as information by the devices 511, 513for the receipt of input signals, and may be converted into signals thatmay be processed by the calculation unit 501. These signals are thenprovided to the calculation unit 501. The devices 512, 514 for sendingoutput signals are arranged to convert the calculation result from thecalculation unit 501 into output signals for transfer to other parts ofthe vehicle's control system, and/or the component(s) for which thesignals are intended.

Each one of the connections to the devices for receiving and sending ofinput and output signals may consist of one or several of a cable; adata bus, such as a CAN (Controller Area Network) bus, a MOST (MediaOriented Systems Transport) bus, or any other bus configuration; or of awireless connection.

A person skilled in the art will realize that the above-mentionedcomputer may consist of the calculation unit 501, and that theabove-mentioned memory may consist of the memory unit 502.

Generally, control systems in modern vehicles consist of acommunications bus system, consisting of one or several communicationsbuses to connect a number of electronic control devices (ECUs), orcontrollers, and different components localised on the vehicle. Such acontrol system may comprise a large number of control devices, and theresponsibility for a specific function may be distributed among morethan one control device. Vehicles of the type shown thus often comprisesignificantly more control devices than what is shown in FIG. 5, whichis well known to a person skilled in the art within the technology area.

As a person skilled in the art will realize, the control device 500 inFIG. 5 may comprise one or several of the control devices 115 and 160 inFIG. 1, the control device 260 in FIG. 2, the control device 360 in FIG.3 and the control device 374 in FIG. 3.

The present invention, in the embodiment shown, is implemented in thecontrol device 500. The invention may, however, also be implementedwholly or partly in one or several other control devices, alreadyexisting in the vehicle, or in a control device dedicated to the presentinvention.

A person skilled in the art will also realize that the above exhausttreatment system may be modified according to the different embodimentsof the method according to the invention. In addition, the inventionrelates to the motor vehicle 100, for example a car, a truck or a bus,or another unit comprising at least one exhaust treatment systemaccording to the invention, such as for example a vessel or avoltage/current-generator.

The present invention is not limited to the embodiments of the inventiondescribed above, but relates to and comprises all embodiments within thescope of the enclosed independent claims.

1. An exhaust treatment system arranged for treatment of an exhauststream, which results from a combustion in a combustion engine, saidsystem comprising: a first dosage device, arranged to supply a firstadditive into said exhaust stream; a first reduction catalyst device,arranged downstream of said first dosage device, and arranged forreduction of nitrogen oxides NO_(x) in said exhaust stream through theuse of said first additive; a particulate filter, at least partlycomprising a catalytically oxidizing coating, which is arrangeddownstream of said first reduction catalyst device, and is arranged tocatch and oxidize soot particles, and to oxidize one or several ofnitrogen oxide NO and incompletely oxidized carbon compounds in saidexhaust stream); a second dosage device, arranged downstream of saidparticulate filter, and arranged to supply a second additive into saidexhaust stream; and a second reduction catalyst device, arrangeddownstream of said second dosage device, and arranged for reduction ofnitrogen oxides NO_(x) in said exhaust stream through the use of atleast one of said first and said second additive.
 2. An exhausttreatment system according to claim 1, wherein at least one of saidfirst and second additives comprises ammonia, or a substance from whichammonia may be extracted and/or released.
 3. An exhaust treatment systemaccording to claim 1, wherein said first reduction catalyst devicecomprises one from among the group of: a first selective catalyticreduction catalyst (SCR₁); a first selective catalytic reductioncatalyst (SCR₁), integrated downstream with a first slip-catalyst (SC₁),wherein said first slip-catalyst (SC₁) is arranged to oxidize oxidise aresidue of additive, and/or to assist said first selective catalyticreduction catalyst (SCR₁) with an additional reduction of nitrogenoxides NO_(x) in said exhaust stream; a first selective catalyticreduction catalyst (SCR₁), followed downstream by a separate firstslip-catalyst (SC₁), wherein said first slip-catalyst (SC₁) is arrangedto oxidize a residue of additive, and/or to assist said first selectivecatalytic reduction catalyst (SCR₁) with an additional reduction ofnitrogen oxides NO_(x) in said exhaust stream; a first slip-catalyst(SC₁), integrated downstream with a first selective catalytic reductioncatalyst (SCR₁), wherein said first slip-catalyst (SC₁) is arranged tooxidize additive, and/or to assist said first selective catalyticreduction catalyst (SCR₁) with a reduction of nitrogen oxides NO_(x) insaid exhaust stream; a first slip-catalyst (SC₁), followed downstream bya separate first selective catalytic reduction catalyst (SCR₁), whereinsaid first slip-catalyst (SC₁) is arranged to oxidize additive, and/orto assist said first selective catalytic reduction catalyst (SCR₁) witha reduction of nitrogen oxides NO_(x) in said exhaust stream; a firstslip-catalyst (SC₁), integrated downstream with a first selectivecatalytic reduction catalyst (SCR₁), integrated downstream with anadditional first slip-catalyst (SC_(1b)), wherein said firstslip-catalyst (SC₁), and/or said additional first slip-catalyst(SC_(1b)), is arranged to oxidize additive, and/or to assist said firstselective catalytic reduction catalyst (SCR₁) with a reduction ofnitrogen oxides NO_(x) in said exhaust stream; a first slip-catalyst(SC₁), followed downstream by a separate first selective catalyticreduction catalyst (SCR₁), followed downstream by a separate additionalfirst slip-catalyst (SC_(1b)), wherein said first slip-catalyst (SC₁),and/or said additional first slip-catalyst (SC_(1b)), is arranged tooxidize additive, and/or to assist said first selective catalyticreduction catalyst (SCR₁) with a reduction of nitrogen oxides NO_(x) insaid exhaust stream; a first slip-catalyst (SC₁), integrated downstreamwith a first selective catalytic reduction catalyst (SCR₁), followeddownstream by a separate additional first slip-catalyst (SC_(1b)),wherein the first slip-catalyst (SC₁), and/or the additional firstslip-catalyst (SC_(1b)), is arranged primarily to reduce nitrogen oxidesNO_(x), and secondarily to oxidize additive in the exhaust stream; afirst slip-catalyst (SC₁), followed downstream by a separate firstselective catalytic reduction catalyst (SCR₁), integrated downstreamwith a separate additional first slip-catalyst (SC_(1b)), wherein thefirst slip-catalyst (SC₁), and/or the additional first slip-catalyst(SC_(1b)), is arranged primarily to reduce nitrogen oxides (NO_(x)), andsecondarily to oxidize additive in the exhaust stream; a firstslip-catalyst (SC₁), which is arranged primarily to reduce nitrogenoxides NO_(x), and secondarily to oxidize additive in said exhauststream; a first selective catalytic reduction catalyst (SCR₁) combinedwith a purely oxidizing coating in its outlet part; a firstslip-catalyst (SC₁), integrated downstream with a first selectivecatalytic reduction catalyst (SCR₁) combined with a purely oxidizingcoating in its outlet part, wherein said first slip-catalyst (SC₁) isarranged primarily to reduce nitrogen oxides NO_(x), and secondarily tooxidize additive in said exhaust stream; and a first slip-catalyst(SC₁), followed downstream by a separate first selective catalyticreduction catalyst (SCR₁) combined with a purely oxidizing coating inits outlet part, wherein said first slip-catalyst (SC₁) is arrangedprimarily to reduce nitrogen oxides NO_(x), and secondarily to oxidizeadditive in said exhaust stream.
 4. An exhaust treatment systemaccording to claim 1, wherein said second reduction catalyst devicecomprises one from among the group of: a second selective catalyticreduction catalyst (SCR₂); a second selective catalytic reductioncatalyst (SCR₂), integrated downstream with a second slip-catalyst(SC₂), wherein said second slip-catalyst (SC₂) is arranged to oxidize aresidue of additive, and/or to assist said second selective catalyticreduction catalyst (SCR₂) with an additional reduction of nitrogenoxides NO_(x) in said exhaust stream; and a second selective catalyticreduction catalyst (SCR₂), followed downstream by a separate secondslip-catalyst (SC₂), wherein said second slip-catalyst (SC₂) is arrangedto oxidize a residue of additive, and/or to assist said second selectivecatalytic reduction catalyst (SCR₂) with an additional reduction ofnitrogen oxides NO_(x) in said exhaust stream.
 5. An exhaust treatmentsystem according to claim 1, wherein said particulate filter is thefirst exhaust treatment system component, which said exhaust streamreaches after having passed said first reduction catalyst device.
 6. Anexhaust treatment system according to claim 1, wherein said exhausttreatment system comprises a system for supply of additive, whichcomprises at least one pump, arranged to supply said first and seconddosage device with said first and second, additive, respectively.
 7. Anexhaust treatment system according to claim 6, wherein said system forsupply of additive comprises a dosage control device, arranged tocontrol said at least one pump.
 8. An exhaust treatment system accordingto claim 6, wherein said system for supply of additive comprises adosage control device, comprising: a first pump control device, arrangedto control said at least one pump, wherein a first dosage of said firstadditive is supplied to said exhaust stream through the use of saidfirst dosage device; and a second pump control device, arranged tocontrol said at least one pump, wherein a second dosage of said secondadditive is supplied to said exhaust stream through the use of saidsecond dosage device.
 9. An exhaust treatment system according to claim1, wherein said first reduction catalyst device is arranged for thereduction of said nitrogen oxides NO_(x) within a reduction temperatureinterval T_(red), which at least partly differs from an oxidationtemperature interval T_(ox), within which said particulate filter isarranged for oxidation of incompletely oxidized carbon compounds;T_(red)≠T_(ox).
 10. An exhaust treatment system according to claim 1,wherein said first reduction catalyst device constitutes an, at leastpartly, protective substrate, upstream of a catalytically oxidizingcoating.
 11. An method for treatment of an exhaust stream, which resultsfrom a combustion in a combustion engine, said method comprising:controlling a supply of a first additive into said exhaust streamthrough the use of a first dosage device, wherein said supply of saidfirst additive impacts a reduction of nitrogen oxides NO_(x) in saidexhaust stream, through the use of said first additive in at least onefirst reduction catalyst device, arranged downstream of said firstdosage device; catching and oxidizing of soot particles, and oxidizingof one or several of nitrogen oxide NO and incompletely oxidizedoxidised carbon compounds in said exhaust stream, through the use of aparticulate filter, at least partly comprising a catalytically oxidizingcoating, which is arranged downstream of said first reduction catalystdevice; and controlling supply of a second additive into said exhauststream through the use of a second dosage device, arranged downstream ofsaid particulate filter, wherein said supply of said second additiveimpacts a reduction of nitrogen oxides NO_(x) in said exhaust streamthrough the use of at least one of said first and said second additivein a second reduction catalyst device, arranged downstream of saidsecond dosage device.
 12. An method according to claim 11, wherein saidcombustion engine is controlled to generate heat, for heating of saidfirst reduction catalyst device to such an extent that said firstreduction catalyst device reaches a predetermined temperature.
 13. Anmethod according to claim 11, wherein said reduction by way of saidfirst reduction catalyst device is controlled to occur within areduction temperature interval T_(red), which at least partly differsfrom an oxidation temperature interval T_(ox), within which saidoxidation of incompletely oxidized carbon compounds, by way of saidparticulate filter, occurs; T_(red)≠T_(ox).
 14. An method according toclaim 11, wherein said supply of at least one of said first and secondadditives, through the use of one of said first dosage device and saidsecond dosage device, respectively, is increased to a level at whichthere is a risk of precipitates of said additive arising.
 15. An methodaccording to claim 14, wherein said first reduction catalyst devicecomprises a first slip-catalyst (SC₁), which primarily carries out areduction of nitrogen oxides NO_(x), and secondarily carries outoxidation of a residue of additive in said exhaust stream.
 16. An methodaccording to claim 11, wherein said supply of at least one of said firstand second additive, through the use of one of said first dosage deviceand said second dosage device, respectively, is reduced, following whichresidues of at least one of said first and second additives areeliminated by heat in said exhaust stream, wherein said reducing of saidsupply is carried out, if the required total catalytic function for anexhaust treatment system carrying out said method is provided after saidreducing.
 17. An method according to claim 16, wherein said requiredcatalytic function depends on currently measured and/or predictedoperating conditions for said combustion engine.
 18. An method accordingto claim 16, wherein said reducing of said supply constitutes aninterruption of said supply.
 19. An method according to claim 11,wherein said impact on said reduction of nitrogen oxides NO_(x) for saidfirst reduction catalyst device is controlled, based on one or severalcharacteristics and/or operating conditions for said first reductioncatalyst device.
 20. An method according to claim 11, wherein saidimpact on said reduction of nitrogen oxides NO_(x) for said firstreduction catalyst device is controlled, based on one or severalcharacteristics and/or operating conditions for said second reductioncatalyst device.
 21. An method according to claim 11, wherein saidimpact on said second reduction catalyst device is controlled, based onone or several characteristics and/or operating conditions for saidsecond reduction catalyst device.
 22. An method according to claim 11any of claims 11-18, wherein said impact on said second reductioncatalyst device is controlled, based on one or several characteristicsand/or operating conditions for said first reduction catalyst device.23. An method according to claim 19, wherein said characteristics forsaid first and second reduction catalyst devices, respectively, arerelated to one or several from among the group of: catalyticcharacteristics for said first reduction catalyst device; catalyticcharacteristics for said second reduction catalyst device; a catalysttype for said first reduction catalyst device; a catalyst type for saidsecond reduction catalyst device; a temperature interval within whichsaid first reduction catalyst device is active; a temperature intervalwithin which said second reduction catalyst device is active; anammoniac coverage degree for said first reduction catalyst device; andan ammoniac coverage degree for said second reduction catalyst device.24. An method according to claim 11, wherein said first reductioncatalyst device constitutes a substrate, which at least partly protectsa catalytically oxidizing coating.
 25. An method according to any ofclaims 11-24, wherein said first reduction catalyst device carries out afirst reduction of a first amount of said nitrogen oxides NO_(x) _(_) ₁reaching said first reduction catalyst device; said second reductioncatalyst device carries out a second reduction of a second amount ofsaid nitrogen oxides NO_(x) _(_) ₂ reaching said second reductioncatalyst device; and an adaptation is carried out of a ratio NO₂ _(_)₂/NO_(x) _(_) ₂, between an amount of nitrogen dioxide NO₂ _(_) ₂ andsaid second amount of nitrogen oxides NO_(x) _(_) ₂ reaching said secondreduction catalyst device, wherein an active control of said firstreduction of said first amount of nitrogen oxides NO_(x) _(_) ₁ iscarried out, based on a value for said ratio NO₂ _(_) ₂/NO_(x) _(_) ₂.26. An method according to claim 25, wherein said value for said ratioNO₂ _(_) ₂/NO_(x) _(_) ₂ consists of one from among the group: ameasured value; a modelled value; and a predicted value.
 27. (canceled)28. A computer program product comprising computer program code storedon a non-transitory computer readable medium, said computer programproduct for treatment of an exhaust stream, which results from acombustion in a combustion engine, said computer program code comprisingcomputer instructions to cause one or more computer processors toperform the operations of: controlling a supply of a first additive intosaid exhaust stream through the use of a first dosage device, whereinsaid supply of said first additive impacts a reduction of nitrogenoxides NO_(x) in said exhaust stream, through the use of said firstadditive in at least one first reduction catalyst device, arrangeddownstream of said first dosage device; catching and oxidizing of sootparticles, and oxidizing of one or several of nitrogen oxide NO andincompletely oxidized carbon compounds in said exhaust stream, throughthe use of a particulate filter, at least partly comprising acatalytically oxidizing coating, which is arranged downstream of saidfirst reduction catalyst device; and controlling supply of a secondadditive into said exhaust stream through the use of a second dosagedevice, arranged downstream of said particulate filter, wherein saidsupply of said second additive impacts a reduction of nitrogen oxidesNO_(x) in said exhaust stream, through the use of at least one of saidfirst and said second additive in a second reduction catalyst device,arranged downstream of said second dosage device.